drm/amdgpu: cleanup ring/ib test for SRIOV vcn2.0 (v2)

support IB test on dec/enc ring
disable ring test on dec/enc ring (MMSCH limitation)

v2: squash in unused variable warning fix

Singed-off-by: darlington Opara <darlington.opara@amd.com>
Signed-off-by: Jinage Zhao <jiange.zhao@amd.com>
Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Acked-by: Leo Liu <leo.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>