power, workqueue: remove keventd_up() usage

Now that workqueue can handle work item queueing/cancelling from very
early during boot, there is no need to gate cancel_delayed_work_sync()
while !keventd_up().  Remove it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Qiao Zhou <qiaozhou@asrmicro.com>