boards: arm: arty: add missing default for enabling SPI support
boards: arm: arty: add missing default for enabling SPI support

Add missing default for enabling CONFIG_SPI if CONFIG_FLASH is
enabled. This is needed for CONFIG_SPI_NOR.

Signed-off-by: Henrik Brix Andersen <a076b11c2cc63ccdc903dbe182e1eecc3cbbc094@brixandersen.dk>

finikorg/zephyr,finikorg/zephyr,Vudentz/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,Vudentz/zephyr,Vudentz/zephyr,Vudentz/zephyr,nashif/zephyr,finikorg/zephyr,Vudentz/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,nashif/zephyr,galak/zephyr,galak/zephyr,nashif/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr