samples: flash_shell: skip boards without zephyr,flash-controller
samples: flash_shell: skip boards without zephyr,flash-controller

Adjust the sanitycheck filter of the flash shell sample to also depend
on the board having a chosen zephyr,flash-controller devicetree node (as
this is what is referenced in flash_shell.c).

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

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