AudioService: allow volume control on analog dock

This re-enables volume control on some Motorola docks.

Change-Id: If7751867de2c0cefb5a8518b5a6a607a9676b946
Revert "Revert "Squashed commit of audio changes from CodeAurora""

This reverts commit 5673983926fd1304d0c7138c1c694f403c2db266.