IB/mthca: 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 "catas_wq" in triggering a device remove and causing a
device reset when a catastrophic error occurs. 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>
Signed-off-by: Doug Ledford <dledford@redhat.com>