scsi: mptfc: Remove deprecated create_singlethread_workqueue

The workqueue "fc_rescan_work_q" queues multiple work items viz
&ioc->fc_rescan_work, &ioc->fc_lsc_work, &ioc->fc_setup_reset_work,
which require strict execution ordering.  Hence, an ordered dedicated
workqueue has been used.

WQ_MEM_RECLAIM has been set since the workqueue is belongs to a storage
driver which is being used on a memory reclaim path and hence, requires
forward progress under memory pressure.

Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>