AudioService: support "full volume devices"

When CEC sink is found, add DEVICE_OUT_HDMI to the list of
  full volume devices (and remove it from fixed vol devices).
Check whether device is full volume when adjusting volume:
  - don't show UI
  - don't check whether volume index changed
When setting stream volume and device is full volume: don't
  change volume index.

This change enables plugging the Android TV device to
  non-CEC devices and have variable volume with UI, and
  to CEC devices with full volume behavior.

Bug: 130830042
Test: change volume on device, verify command goes to CEC with "adb shell dumpsys hdmi_control"
Change-Id: I92bc3f7a13e3cf04b45d6c2cf8a49c0eac0657c0