PowerManager: Introduce PowerExt supported boosting APIs

* These new APIs allow for boosting via custom
  and arbitrary hints such as Fling, Animation, etc.

* The first supported custom hint will be,
  FLING_BOOST, followed by other implementations
  in the future.

Signed-off-by: betaxab <betaxab@gmail.com>
Signed-off-by: electimon <electimon@gmail.com>
Change-Id: Ieeeb821418df3c6af2d51115f9c30c6207dfd527