drm/amdgpu: add initial VCN2.0 support (v2)

VCN (Video Core Next) is the video encode/decode block.

Porting over the same functions from VCN1.0

v2: squash in updates (Alex)

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