Issue 5256795: Phone ringtone volume is too low

Modified the volume curve for ringtones and notifications
in audio policy manager. The first volume step now corresponds to
-30dB instead of -50dB thus making ringtone much more
audible for low volume settings.

Also made a generic implementation of volume curves according to
audio policy strategies.

Change-Id: Ieb7916ba2e53c2a10a47efec82814cabed21c48b
2 files changed