sdm: Add support for CPU hint

- Set the hint when there is only one updating layer, which helps
  in reducing CPU clock and thus power.
- This feature is enabled with the property sdm.perf_hint_window,
  which is set to a positive value, which will be the window of frames
  to skip before the hint is set.

CRs-fixed: 853602
Change-Id: I1af21551510f99752c0b6bbfec3e5c75880c3ab2
8 files changed