Support for delayed audio focus

New internal API for an audio focus requester to always enter
 the audio focus stack even if audio focus can't be granted
 immediately (e.g. during a phone call).
Remap the "no delay" interface to the new "requestAudioFocus"
 method signature and AIDL.

Bug 16010554

Change-Id: Iff91ddb0beb411cca1f8cf98300a9afc4178dc7f