IB/mlx5/odp: Remove deprecated create_singlethread_workqueue

alloc_ordered_workqueue() with WQ_MEM_RECLAIM set, replaces
deprecated create_singlethread_workqueue(). This is the identity
conversion.

The workqueue "mlx5_ib_page_fault_wq" queues work item &qp_pfault->work.
It has been identity converted.

WQ_MEM_RECLAIM has been set to ensure forward progress under
memory pressure.

Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
Acked-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>