drm/amdgpu/vg20:Enable 2nd instance queue maping for uvd 7.2

Enable 2nd instance uvd queue maping for uvd 7.2. For user, only one UVD
instance presents. there is two rings for uvd decode, and
4 rings for uvd encode.

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