Bluetooth: Remove deprecated create_singlethread_workqueue

The workqueue "workqueue" queues multiple work items viz &qca->ws_awake_rx
&qca->ws_rx_vote_off, &qca->ws_awake_device, &qca->ws_tx_vote_off which
require strict execution ordering. Hence, an ordered dedicated workqueue
has been used to replace the deprecated create_singlethread_workqueue
instance.

WQ_MEM_RECLAIM has not been set since the driver is not being used on a
memory reclaim path.

Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>