alloc_workqueue replaces deprecated create_workqueue().

Since the driver is infiniband which can be used as block device and the
workqueue seems involved in regular operation of the device, so a
dedicated workqueue has been used  with WQ_MEM_RECLAIM set to guarantee
forward progress under memory pressure.
Since there are only a fixed number of work items, explicit concurrency
limit is unnecessary here.
Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>