bluetooth: Modular API for A2DP codecs

bluetooth: Modular API for A2DP codecs

This patch introduce new modular API for bluetooth A2DP codecs. Its
benefits are:

* bluez5-util and module-bluez5-device does not contain any codec specific
  code, they are codec independent.

* For adding new A2DP codec it is needed just to adjust one table in
  a2dp-codec-util.c file. All codec specific functions are in separate
  codec file.

* Support for backchannel (microphone voice). Some A2DP codecs (like
  FastStream or aptX Low Latency) are bi-directional and can be used for
  both music playback and audio call.

* Support for more configurations per codec. This allows to implement low
  quality mode of some codec together with high quality.

Current SBC codec implementation was moved from bluez5-util and
module-bluez5-device to its own file and converted to this new A2DP API.