hal: add support to separate headset and headphones mixer backend
am: 9536e67b03

Change-Id: Id4b90deb5e0d18e1606e71a175a882e1501415f9
tree: 23ed8389e921e3a84a71266b22a37538d168c55c
  1. hal/
  2. legacy/
  3. post_proc/
  4. visualizer/
  5. voice_processing/
  6. Android.mk