subsys: power: Add OS managed Power Management framework

Add support for OS managed Power Management framework for Zephyr
under 'subsys/power'. This framework takes care of implementing
the _sys_soc_suspend/_sys_soc_resume API's, a PM policy based on
SoC Low Power residencies and also provides necessary API's to
do devices suspend and resume.

Also add necessary changes to support the existing Application
managed Power Management framework.

Signed-off-by: Ramakrishna Pallala <ramakrishna.pallala@intel.com>