drm/amdgpu: stop adding VM updates fences to the resv obj

Don't add the VM update fences to the resv object and remove
the handling to stop implicitely syncing to them.

Ongoing updates prevent page tables from being evicted and we manually
block for all updates to complete before releasing PDs and PTS.

This way we can do updates even without the resv obj locked.

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