msm: hotplug: Add pm ops
msm: hotplug: Fix symbol export
msm: hotplug: Fixup sysfs interface

* Use proper return values
* Fix store_down_lock_duration()
* Add some more checks
* Cleanup some mess
msm: hotplug: Update threshold values and down lock duration

* Power up additional cpus earlier
* Power down cpus later
* Keep cpus online at least 5 seconds