PM: wakeup: expose pm_wakeup_pending to modules

intel_pch_thermal driver needs a long delay to cool itself (60 seconds
in maximum) during suspend. When a wakeup event occures during the
delay, it is better for the intel_pch_thermal driver to detect this and
quit cooling because the suspend is likely to abort anyway.

Thus expose pm_wakeup_pending to modules so that intel_pch_thermal
driver can be aware of the wakeup events.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Tested-by: Sumeet Pawnikar <sumeet.r.pawnikar@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>