PowerOP, Whatchanged/Issues/TODO 3/3

whatchanged:
- interface to get list of registered operating point names is added
- notification callbacks interface on point registration/unregistration is added
- registration of a point with duplicated name fix

todo/issues:
- better implementation for for getting registered operating point names
- move string parsing into powerop generic code
- power parameter names export
- configfs for operating points creation from user space