feat(plat/imx8m): add system_reset2 implementation

Add imx_system_reset2 which extends existing SYSTEM_RESET. It provides
architectural reset definitions and vendor-specific resets.
By default warm reset is triggered.

Also refactor existing implementation of wdog reset, add details about
each flag used.

Change-Id: Ia7348c32c385f1c61f8085776e81dd1e38ddda5c
Signed-off-by: Igor Opaniuk <igor.opaniuk@foundries.io>
4 files changed