ARC: mwdt: add __fallthrough attribute support
ARC: mwdt: add __fallthrough attribute support

As we set the minimal required version of ARC MWDT to 2022.06
we can add __fallthrough attribute

Signed-off-by: Eugeniy Paltsev <ec089b543c2604b626d7ce60c03e4d074ed102c7@synopsys.com>
Signed-off-by: Evgeniy Paltsev <7de4ab8b01334d64e4e84734c688a8a936513edc@gmail.com>

zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,galak/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr