power: ab8500_btemp: Remove deprecated create_singlethread_workqueue

The workqueue "btemp_wq" is used for measuring the temperature
periodically. It queues a single workitem (btemp_periodic_work) and
hence doesn't require ordering. Thus, the deprecated
create_singlethread_workqueue() instance has been replaced with
alloc_workqueue().

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

Since there is a single work item, explicit concurrency
limit is unnecessary here.

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