boards: arm: reduce the default drivers for the Arduino Zero

Now that the SAM0 SOC selects the appropriate SAM0 driver for a class,
reduce the drivers that are compiled in by default on the Arduino
Zero.  This reduces the size of `blink` from ~14 KiB to ~10 KiB.

Also add the supported features to arduino_zero.yaml to get more
coverage in the sanity tests.

Signed-off-by: Michael Hope <mlhx@google.com>

boards/arm/arduino_zero/arduino_zero.yaml

@@ -8,3 +8,14 @@ toolchain:
   - zephyr
   - gnuarmemb
   - xtools
+supported:
+  - adc
+  - counter
+  - dma
+  - gpio
+  - hwinfo
+  - pinmux
+  - spi
+  - uart
+  - usb_device
+  - watchdog

boards/arm/arduino_zero/arduino_zero_defconfig

@@ -6,19 +6,8 @@ CONFIG_BOARD_ARDUINO_ZERO=y
 CONFIG_CORTEX_M_SYSTICK=y
 CONFIG_CONSOLE=y
 CONFIG_UART_CONSOLE=y
-CONFIG_SERIAL=y
-CONFIG_UART_SAM0=y
 CONFIG_UART_INTERRUPT_DRIVEN=y
-CONFIG_GPIO=y
-CONFIG_GPIO_SAM0=y
-CONFIG_WATCHDOG=y
-CONFIG_WDT_SAM0=y
+CONFIG_SERIAL=y
+CONFIG_PINMUX=y
 CONFIG_SOC_ATMEL_SAMD_XOSC32K=y
 CONFIG_SOC_ATMEL_SAMD_XOSC32K_AS_MAIN=y
-CONFIG_SPI=y
-CONFIG_SPI_SAM0=y
-CONFIG_SPI_4=y
-CONFIG_PINMUX=y
-CONFIG_PINMUX_SAM0=y
-CONFIG_USB=y
-CONFIG_USB_DC_SAM0=y