drm/amdgpu/vcn: move macro from vcn2.0 to share amdgpu_vcn (v2)

Move macro from vcn2.0 to amdgpu_vcn to share with vcn2.5

v2: squash in macro fix

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