CEC: Let playback device send <Standby> upon power off

Let playback device send a command <Standby> based on the setting.
ACTION_SHUTDOWN leads to broadcast command to put all the devices
to sleep, and ACTION_SCREEN_OFF optionally turns off TV only.

Change-Id: Id458b23ce86b0c3179efa21cce85b721a47001be
4 files changed