PowerManager: Adds the Sustained performance API.

Adds a new type of wakelock - SUSTAINED_PERFORMANCE_WAKELOCK. This
wakelock can only be acquired when the application is in the foreground.
And it is not effective when the application is no longer in the
foreground.

Acquiring this wakelock enables the Sustained performance mode which
guarantees a certain level of performance.

Bug: 22864186

Change-Id: Id0ececc756fe014779db6efde7aede23ea181dc5
Signed-off-by: Ruchi Kandoi <kandoiruchi@google.com>