Revert "drm/amdgpu: don't attach the tlb fence for SI"

Revert "drm/amdgpu: don't attach the tlb fence for SI"

This reverts commit 820b3d376e8a102c6aeab737ec6edebbbb710e04.

It’s better to validate VM TLB flushes in the flush‑TLB backend
rather than in the generic VM layer.

Reverting this patch depends on
commit fa7c231fc2b0 ("drm/amdgpu: validate the flush_gpu_tlb_pasid()")
being present in the tree.

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