IB/mlx5: Remove deprecated create_singlethread_workqueue

IB/mlx5: 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 "cache->wq" queues work items &ent->work (maps to
cache_work_func) and &ent->dwork(maps to delayed_cache_work_func).
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>
Acked-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>