ACPI works need to be executed on cpu0 and acpi/osl.c achieves this by
creating singlethread workqueue and then binding it to cpu0 from a
work which is quite unorthodox.  Make it create regular workqueues and
use queue_work_on() instead.  This is in preparation of concurrency
managed workqueue and the extra workers won't be a problem after it's
implemented.
Signed-off-by: Tejun Heo <tj@kernel.org>