m7-common: Add low latency audio usecases

Change-Id: Ibd91e286d8b05d3aba65f2e8edebeb291297a9e4
m7-common: use low latency audio_policy.conf

Change-Id: I79e6af7c48d08b72815382a90480867d5819034b
m7-common: set amplifier configs based on audio mode

Depends on: http://review.cyanogenmod.org/#/c/38256/

Change-Id: Icadd71698144c120dbb26282da4e138a4d8a07d1