drm/amdgpu/vcn2: notify SMU power up/down VCN

For sw control power gating, it needs notify SMU to power up/down VCN
when enter/exit working state.

Signed-off-by: Jack Xiao <Jack.Xiao@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>