PM / Runtime: Use alloc_workqueue() for creating the PM workqueue

Although we need the PM workqueue to be freezable, we don't need it
to be singlethread.  Also, the number of concurrent work items
running on a single CPU need not be constrained.  For these reasons
use alloc_workqueue() directly, with suitable arguments, instead of
create_freezeable_workqueue(), to create the runtime PM workqueue.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Tejun Heo <tj@kernel.org>

kernel/power/main.c

@@ -308,7 +308,7 @@ EXPORT_SYMBOL_GPL(pm_wq);
 
 static int __init pm_start_workqueue(void)
 {
-	pm_wq = create_freezeable_workqueue("pm");
+	pm_wq = alloc_workqueue("pm", WQ_FREEZEABLE, 0);
 
 	return pm_wq ? 0 : -ENOMEM;
 }