drm/amdgpu/virt: bypass cg and pg setting for SRIOV

GPU hypervisor cover all settings of CG and PG, so guest doesn't
need to do anything. Bypass it.

Signed-off-by: Frank Min <Frank.Min@amd.com>
Signed-off-by: Xiangliang Yu <Xiangliang.Yu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>