Adding AIDL version 2 of AudioControl HAL

- Updated APIs to use PlaybackTrackMetadata (aka AudioAttributes)
instead of usage to get rid of usages list limitation.

- Add Gain Callback to notify unexpected gain changed from HAL
(as currently done for Audio Focus).

- Aggregate Callbacks within a unique IAudioControlCallback interface

Bug: b/154906631
Test: build and run VTS tests

Signed-off-by: Francois Gaffie <francois.gaffie@renault.com>
Change-Id: If74d575fad3888b698250a8ec9a6918f7cb294d7
Merged-In: If74d575fad3888b698250a8ec9a6918f7cb294d7