drivers: flash: gecko: Add support for Gecko Series 2 SoC
drivers: flash: gecko: Add support for Gecko Series 2 SoC

The EFR32MG21 SoC uses MSC_LOCK_LOCKKEY_UNLOCK instead of
MSC_UNLOCK_CODE.

Signed-off-by: Steven Lemaire <278ad34154d48931a1fe98a95620ecd011bfd217@zii.aero>

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