cec: support standby features for tx/rx [1/1]

cherrypick ag/4808863

Bug: 112553298

When press power key on soundbar, CEC type is 5(audio system),
it will send command to tx and rx devices to let them go to standby mode

Test: Tested with a TV
Change-Id: I242fb1028b5ae003e6054fe9b54e10d1f433374c