drm/amdgpu: don't use MM idle_work for SRIOV(v2)

SRIOV doesn't give VF cg/pg feature so the MM's idle_work
is skipped for SR-IOV

v2:
remove superfluous changes
since idle_work is not scheduled for SR-IOV so the condition
check for SR-IOV inside idle_work also can be dropped

v3:
drop the SRIOV check in amdgpu_vce/uvd_suspend

Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>