[2/2] Improve led availability checking and caching.

* This continues the work done in frameworks. Btw this mod is used only for our rom (PA),
  if so it will need same variable defined in Settings.java or another one. If not will use
  the method to invoke the camera instance and verify. Doesn't broke anything but speed up
  the check for us.
* Depends on related frameworks/base change.

Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>