drm/amdgpu: add support to power up/down UMSCH by SMU

Power up/down UMSCH by SMU.

Signed-off-by: Lang Yu <Lang.Yu@amd.com>
Acked-by: Leo Liu <leo.liu@amd.com>
Acked-by: Veerabadhran Gopalakrishnan <Veerabadhran.Gopalakrishnan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>