Adding an API to report sound trigger events

Sound trigger events can wake the CPU up. Adding an API that can be used
by the sound trigger modules to report whenever the underlying hardware
notifies the main chip on recognizing a phrase.

The API is non-functional now. Functionality will be added once the
event has been piped from the SoundTrigger system.

Test: Builds, boots.

Bug: 267717665
Change-Id: Id6382aa2f2b09cde0a2fda728c0825e3a5d15a3d