Revamp HDMI-CEC system audio mode integration with audio service.

In previous change we use setForceUse(FORCE_MEDIA, XXX) method
in order to set specific audio output type, such as LINE, HDMI_ARC,
and SPDIF. But it turns out that it conflicts with bluetooth
a2dp which uses the same setForceUse(FORCE_MEDIA, yyy).

This change is based on several conditions.

1. When other non-speaker devices are on, prevent system audio
   from turing on.
2. In order to keep track of other devices' connectivity and to
   turn off system audio if other device like bluetooth or
   headphone preempts current output, register OnAudioPortChangeListner
   to audio manager.
3. All possible system audio outputs can be merged with other
   outputs without priority.

Change-Id: Id4e47d99db64b9f77a17c2c28c47787ab8980bf7