Send <Report audio status> CEC commands when it's changed

According to HDMI CEC specification, an audio system
can report its audio status when System Audio Mode
is on, so that the TV can display the audio status
of external amplifier.

More details can be found in section CEC-13.15 of
HDMI Specification 1.4b

Bug: 80297383
Test: make; flashall; local tests
Change-Id: Id71b709a62add7bf5dccb418489e200350debb8e