SurfaceFlinger: Add support for extendedMode

- Displays only video with full screen on External with no UI controls
- Primary will show only UI controls
- Similar to presentation class, but will be used by a third
  party app, which does not use presentation class
- To enable this set sys.extended_mode to 1

Change-Id: I9a66c770e1c1a7471cb50690514497dae8dad4b3