Add interface for SMU12 device, used by UMR.

v2: fix code style
Signed-off-by: NJinzhou.Su <Jinzhou.Su@amd.com>
Reviewed-by: NEvan Quan <evan.quan@amd.com>
Reviewed-by: NHuang Rui <ray.huang@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>