Sound trigger middleware service definition

These are the AIDL files that define the sound trigger middleware
interface.
This service is intended to replace the existing
frameworks/av/include/soundtrigger/ISoundTriggerHwService.h
using AIDL in order to avoid a large amount of hand-written
parceling code and other forms of boilerplate, and provide
cross-language support.

Change-Id: Ia783ba4f1ea7335a984396e7024cac0411699403
Bug: 142070343