Dynamic audio policies: allow device passing for RENDER mixes

AudioMix: add system method for specifying an AudioDeviceInfo
 to be used by this mix. This only works for AudioMix
 instance with the RENDER route flag.
Previous dynamic policy implementation didn't enforce
 mix route flag check, but only supported LOOP_BACK,
 so make LOOP_BACK the default.
When a policy gets registered and the registration ID is
 set on each mix, for RENDER mixes use the device
 address for registration.

Bug 25448664

Change-Id: If5789d84ff4c4c25a6e81ba1513a39916220498a