beagleconnect_freedom: Add SPI support

- Only supports master mode

Signed-off-by: Ayush Singh <ayushdevel1325@gmail.com>

Author: Ayush1325

variants/beagleconnect_freedom/beagleconnect_freedom.overlay

@@ -50,6 +50,7 @@
  	builtin-led-gpios = <&gpio0 18 GPIO_ACTIVE_HIGH>;	/*  2.4GHz TX/RX  */
  	serials = <&uart0 &uart1>;
  	i2cs = <&i2c0>;
+	spis = <&spi0>;
  };
 };