Revisit HDMI-CEC system audio mode in AudioService.

From recent feedback on HDMI-CEC system audio mode,
it would be unnecessary to enforce output from AudioService.
Instead, it would follow audio policy according to status
of HDMI-CEC system audio mode.
For that removed two params of setHdmiSystemAudioModeSupported
api of AudioManager.

In terms of speaker mute, it will be handled by removing speaker
from audio ouput instead of changing gain control. For that
added new force usage type, FOR_HDMI_SYSTEM_AUDIO_MODE and
new force config type, FORCE_HDMI_SYSTEM_AUDIO_ENFORCED.
This is used to notify change of system audio mode to
audio policy manager.

Bug: 16305986
Bug: 16002150

Change-Id: I5643ad093a651c951e12b567c6e11b88aa87cea2