drm/amdgpu/sriov : Add sriov detection for sienna_cichlid

This is a regression due to the rebase , add sienna_cichlid sriov detection back

Signed-off-by: shaoyunl <shaoyun.liu@amd.com>
Reviewed-by: Likun Gao <Likun.Gao@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>