drm/amdgpu/vcn: Disable CG/PG for SRIOV

For sriov, CG and MG are controlled from hypervisor side,
no need to manage them again in ip init

Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Jane Jian <Jane.Jian@amd.com>
Reviewed-by: Sonny Jiang <sonny.jiang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>