Add hotword detection metrics.

Bug: 207717787
Test: build & boot pass.
Test: manual. Both trust and no-trust still work.
Test: manual. In nornal case, log with expected values, see bug for
details. Log expected value for some error cases (not all are tested)
by local changes.

Change-Id: Iaa778616eca4cfad83a94297d9cd6116bb9577e7