Support NUMAKER_IOT_M263A

1.  Support Nuvoton targets:
    -   NUMAKER_IOT_M263A
2.  Change storage to NUSD (SD card in SDIO bus mode) from SD (SD card SPI bus mode)
    (1) Add COMPONENT_NUSD.lib.
    (2) Add component NUSD (target.components_add).
    (3) Change default BlockDevice to NUSD:
        Override BlockDevice::get_default_instance (nusd.provide-default-blockdevice).
        Required since mbed-cloud-client 2.1.0 (arm_uc_blockdevice_ext) or in:
        mbed-bootloader/modules/storage/pal-blockdevice/source/arm_uc_pal_blockdevice_mbed.cpp
    (4) Enable kvstore with blockdevice type being "other".
        i)  Override get_other_blockdevice() (nusd.provide-kvstore-other-blockdevice).
        ii) Configure storage type to "FILESYSTEM".
        iii)Configure file system type to "LITTLE".
        vi) Configure block device type to "other".
        v)  Configure external size to 64MiB, which cannot overlap with update-client.
            storage-address/update-client.storage-size.
3.  Change back UARTSerial tx/rx buffer size from 1024/1024 to 256/256. This can reduce
    memory footprint by (1024 - 256) * 2 = 1.5KiB. Because this configuration influences
    both ESP8266 and default console (platfrom/mbed_retarget.cpp), memory reduction can
    achieve 1.5KiB x 2 = 3KiB.
4.  Enlarge ESP8266 'send tcp data' timeout on Nuvoton targets
    Pelion connection has some failure rate with this. Enlarging ESP8266_SEND_TIMEOUT
    can just relieve the issue. A ticket has raised to address it:
    ARMmbed/mbed-os#11544

Author: ccli8

README.md

@@ -29,6 +29,7 @@ Board                          |  Connectivity     | Storage for credentials and
 `Nuvoton NUMAKER_PFM_NUC472`        | Ethernet          | SD card (NUSD)          | Build-only
 `Nuvoton NUMAKER_PFM_M487`          | Ethernet          | SD card (NUSD)          | Build-only
 `Nuvoton NUMAKER_IOT_M487`          | Wi-Fi ESP8266     | SD card (NUSD)          | Build-only
+`Nuvoton NUMAKER_IOT_M263A`         | Wi-Fi ESP8266     | SD card (NUSD)          | Build-only
 `Seeed ARCH_MAX`                    | Ethernet          | SD card                 | Build-only
 `Seeed Wio 3G`                      | Cellular          | Internal Flash          | Build-only
 `Renesas RZ_A1H`                    | Ethernet          | External Flash ([See security limitation of this board](https://os.mbed.com/platforms/Renesas-GR-PEACH/#security-limitation-of-this-platform)) | Build-only

bootloader/mbed-bootloader-m263_iot-block_device-kvstore-v4.1.0.bin

@@ -265,6 +265,37 @@
             "esp8266.provide-default"                   : true,
             "target.macros_add"                         : ["MBEDTLS_USER_CONFIG_FILE=\"mbedTLSConfig_mbedOS_SW_TRNG_PSA.h\"", "MBEDTLS_PSA_CRYPTO_C", "MBEDTLS_ENTROPY_NV_SEED", "PAL_USE_HW_TRNG=0", "ESP8266_SEND_TIMEOUT=8000"]
         },
+        "NUMAKER_IOT_M263A": {
+            "target.extra_labels_add"                   : ["PSA"],
+            "target.network-default-interface-type"     : "WIFI",
+            "target.bootloader_img"                     : "bootloader/mbed-bootloader-m263_iot-block_device-kvstore-v4.1.0.bin",
+            "bootloader-size"                           : "(64*1024)",
+            "target.header_offset"                      : "0x12000",
+            "target.app_offset"                         : "0x12400",
+            "target.components_add"                     : ["NUSD"],
+            "nusd.provide-default-blockdevice"          : true,
+            "nusd.provide-kvstore-other-blockdevice"    : true,
+            "update-client.bootloader-details"          : "0x0",
+            "update-client.application-details"         : "0x12000",
+            "update-client.storage-address"             : "(1024*1024*64)",
+            "update-client.storage-size"                : "((MBED_ROM_START + MBED_ROM_SIZE - APPLICATION_ADDR) * MBED_CONF_UPDATE_CLIENT_STORAGE_LOCATIONS)",
+            "update-client.storage-locations"           : 1,
+            "mbed-cloud-client.update-storage"          : "ARM_UCP_FLASHIAP_BLOCKDEVICE",
+            "storage.storage_type"                      : "FILESYSTEM",
+            "storage_filesystem.filesystem"             : "LITTLE",
+            "storage_filesystem.blockdevice"            : "other",
+            "storage_filesystem.internal_base_address"  : "(MBED_ROM_START + MBED_BOOTLOADER_SIZE)",
+            "storage_filesystem.rbp_internal_size"      : "(2*4*1024)",
+            "storage_filesystem.external_base_address"  : "(0x0)",
+            "storage_filesystem.external_size"          : "(1024*1024*64)",
+            "esp8266.tx"                                : "PC_7",
+            "esp8266.rx"                                : "PC_6",
+            "esp8266.rts"                               : "PE_13",
+            "esp8266.cts"                               : "PC_8",
+            "esp8266.rst"                               : "PE_12",
+            "esp8266.provide-default"                   : true,
+            "target.macros_add"                         : ["MBEDTLS_USER_CONFIG_FILE=\"mbedTLSConfig_mbedOS_SW_TRNG_PSA.h\"", "MBEDTLS_PSA_CRYPTO_C", "MBEDTLS_ENTROPY_NV_SEED", "PAL_USE_HW_TRNG=0", "ESP8266_SEND_TIMEOUT=8000"]
+        },
         "DISCO_L475VG_IOT01A": {
             "target.macros_add"                         : ["MBEDTLS_USER_CONFIG_FILE=\"mbedTLSConfig_mbedOS.h\""],
             "target.network-default-interface-type"     : "WIFI",