drm amdgpu: SI UVD v3_1 (v2)

Implement SI UVD. The SI UVD firmware requires validation.

v2: squash in missing brace fix (Colin Ian King)

Signed-off-by: Sonny Jiang <sonny.jiang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>