s390: Remove deprecated create_singlethread_workqueue

The workqueue "appldata_wq" has been replaced with an ordered dedicated
workqueue.

WQ_MEM_RECLAIM has not been set since the workqueue is not being used on
a memory reclaim path.

The adapter->work_queue queues multiple work items viz
&adapter->scan_work, &port->rport_work, &adapter->ns_up_work,
&adapter->stat_work, adapter->work_queue, &adapter->events.work,
&port->gid_pn_work, &port->test_link_work. Hence, an ordered
dedicated workqueue has been used.

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

Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>