os/pm: Add PM Quick Sleep

[gSahitya-samsung]

This PR adds the feature to make board sleep quickly after wakeup. The quick sleep feature is needed to save upmost power when board need to wakeup aperiodically to serve timer expiration callback. For frequent timer expiration case if we do not allow quick sleep then board will remain wakeup for very long time resulting in no power saving.

Note - Now board can sleep immediately after wakeup. It's better to use pm_suspend if application want to suspend board working state.

[edwakuwaku]

@gSahitya-samsung could you please revert ameba_tizenrt_pmu.c/.h? I will make necessary changes in my PR..