usb: dwc2: Remove deprecated create_singlethread_workqueue

alloc_ordered_workqueue replaces the deprecated
create_singlethread_workqueue.

There are multiple work items on the work queue, which require
ordering. Hence, an ordered workqueue has been used.

The workqueue "wq_otg" is not being used on a memory reclaim path.
Hence, WQ_MEM_RECLAIM has not been set.

Acked-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>