boards: arduino: Giga Display Shield, touch points

Currently the config option:
CONFIG_INPUT_GT911_MAX_TOUCH_POINTS

is not defined for the Giga display shield and defaults
to 1.   The valid range is 1-5, I have done most of my
own testing using 3 with the ArduinoGiga-zephyr

I have a PR against the ArduinoCore-zephyr project
which allows me to define a callback in the Arduino
system:
arduino/ArduinoCore-zephyr#134

And a version of the Arduino touch library with some
support, the fork/branch
https://github.com/KurtE/Arduino_GigaDisplayTouch/tree/zephyr

And an example sketch that does touch paint.
arduino/ArduinoCore-zephyr#92 (comment)

Note: my version of the Arduino touch library has no support
for gestures

Signed-off-by: Kurt Eckhardt <kurte@rockisland.com>

Author: KurtE

boards/shields/arduino_giga_display_shield/boards/arduino_giga_r1_m7.conf

@@ -6,3 +6,4 @@ CONFIG_STM32_LTDC_RGB565=y
 CONFIG_DISPLAY_INIT_PRIORITY=87
 CONFIG_STM32_LTDC_DISABLE_FMC_BANK1=y
 CONFIG_INPUT_GT911_INTERRUPT=y
+CONFIG_INPUT_GT911_MAX_TOUCH_POINTS=5