iwlwifi: dvm: use alloc_ordered_workqueue()

Use alloc_ordered_workqueue() to allocate the workqueue instead of
create_singlethread_workqueue() since the latter is deprecated and is scheduled
for removal.

There are work items doing related operations that shouldn't be swapped when
queued in a certain order hence preserve the strict execution ordering of a
single threaded (ST) workqueue by switching to alloc_ordered_workqueue().

WQ_MEM_RECLAIM flag is not needed since the worker is not depended
during memory reclaim.

Signed-off-by: Eva Rachel Retuya <eraretuya@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>