scsi: mpt: Remove deprecated create_singlethread_workqueue

The workqueues "ioc->reset_work_q" and "ioc->fw_event_q" queue a single
work item &ioc->fault_reset_work and &fw_event->work, respectively and
hence don't require ordering. Hence, they have been converted to use
alloc_workqueue().

The WQ_MEM_RECLAIM flag has been set to ensure forward progress under
memory pressure since the workqueue belongs to a storage driver which is
being used on a memory reclaim path.

Since there are fixed number of work items, explicit concurrency limit
is unnecessary here.

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>