power: ds2760_battery: Remove deprecated create_singlethread_workqueue

alloc_ordered_workqueue() with WQ_MEM_RECLAIM set replaces
deprecated create_singlethread_workqueue(). This is the identity
conversion.

The workqueue "monitor_wqueue" is used to monitor the battery
status. It has been identity converted.

It queues multiple work items viz &di->monitor_work,
&di->set_charged_work, which require execution ordering.
Hence, alloc_workqueue has been used to replace the
deprecated create_singlethread_workqueue instance.

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

Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>