IB/addr: Remove deprecated create_singlethread_workqueue

The workqueue "addr_wq" queues a single work item &work and hence
doesn't require ordering. Also, it is being used on a memory reclaim
path. Hence, it has been converted to use alloc_workqueue with
WQ_MEM_RECLAIM set.

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>