Bluetooth: A2DP Sink support for Settings App

- add support for A2DP Sink in Settings App. This will enable connection
  initiation and updation on Settings App
- add framework Apis to support A2DP Sink. Any third party Apps can access
  A2DP Sink priority of device and playing state of device
- add support for key to set priority. This manages priority of device for
  A2DP Sink profile

Change-Id: I9920957e0f20583e1e2d57ca76c2c0bd9dfa0bcf