Vega20 has dual-UVD. Need add multiple instances support for uvd.
Restruct uvd.inst, using uvd.inst[0] to replace uvd.inst->.
Repurpose amdgpu_ring::me for instance index, and initialize to 0.
There are no any logical changes here.
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>