Add for System Audio Mode

Note that this is skeleton change and do not merge
till get full review from outside of CEC team.

This change introduce four apis for System Audio Mode

1. boolean canChangeSystemAudioMode()
  -  Whether to change system audio mode or not.

2. setSystemAudioMode(boolean enabled, IHdmiControlCallback callback);
  - Change system audio mode.

3. add/removeSystemAudioModeChangeLister.
  - Register/deregister listner for AudioModeChange.

4. getSystemAudioMode()
  - Whether to system audio is enabled or not.

Change-Id: I1e82365155a9f7f6c3ac5d9db4871cf6bad46865