It certainly is not a good idea to execute _ON or _OFF and _STA
for the same power resource at the same time which may happen in
some circumstances in theory.  To prevent that from happening,
read the power state of each power resource under its mutex, as
that will prevent the state from being changed at the same time.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Len Brown <len.brown@intel.com>