drm/amdgpu: Ignore stop rlc on SRIOV environment.

For SRIOV, the guest driver should not do stop rlc. The host
handles programing RLC.

On SRIOV, the stop rlc will be hang (RLC related registers are
blocked by policy) when the RLCG interface is not enabled.

Reviewed-by: Yang Wang <kevinyang.wang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Gavin Wan <Gavin.Wan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>