drm/amdgpu/vcn:Always gate vcn block during hw finishing

Under Dynamic Power Gate mode, UVD_STATUS needn't be checked.

Signed-off-by: James Zhu <James.Zhu@amd.com>
Acked-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>