power: pm2301_charger: 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 "charger_wq" is used for running all the charger related
tasks. This involves charger detection, checking for HW failure and HW
status. This workqueue has been identity converted.

It queues multiple workitems viz &pm2->check_main_thermal_prot_work,
&pm2->check_hw_failure_work, &pm2->ac_work. Hence, the deprecated
create_singlethread_workqueue() instance has been replaced with a
dedicated ordered workqueue.

The 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>