Update AudioPolicyManagerBase to only use audio_devices_t

The AudioPolicyManagerBase implementation was using some device
 enum values from AudioSystemLegacy.h, of type audio_devices,
 and some from /system/audio.h, of type audio_devices_t.
Now only uses audio_devices_t, and associated functions to
 inspect what audio device type they correspond to.
Added #define to represent "no audio device" to clarify code.
Removed unused variable in AudioPolicyManagerBase::startOutput()

Change-Id: Ibec311dac550d6a806397377206a43bc708914c0
4 files changed