send SoundTriggerFailure when enrollment prempts session

DSP model enrollment preempts the running SoundTrigger session by
asynchronously stopping an ongoing session. This change makes sure the
client is notified when the enrollment process changes session state.

Test: atest AlwaysOnHotwordDetectorTest
Bug: 272148104
Change-Id: Id22941354c89836a6d5bfdcd6308e64cb863af82