Added specific volume curves for AUDIO_STREAM_SYSTEM,
AUDIO_STREAM_ENFORCED_AUDIBLE and AUDIO_STREAM_DTMF.
Volume for these streams tracks AUDIO_STREAM_RING on phones
and AUDIO_STREAM_MUSIC on tablets but is contrained in the range
-24dB to -6dB on speaker and -24dB to -12dB on headset.
STRATEGY_ENFORCED_AUDIBLE routing policy is now the same as
STRATEGY_MEDIA in countries where not enforced.
Change-Id: If58d96559bfe2bbff4cd94c631d5933bd940778e
ddfe26905e