Define audio policy, mixes, and mixing rules

An AudioMixingRule is a collection of AudioAttributes and match/exclude
   rules.
An AudioMix is defined by its AudioMixingRule, AudioFormat and
   routing flag.
An AudioPolicyConfig is a collection of AudioMix and is
   parcellable.
An AudioPolicy has an AudioPolicyConfig, and
   can be registered/unregistered through AudioManager.

bug 16009464

Change-Id: I01bf95d014967f48ba823648ea897779da099e5d