By popular demands, I add the functionality to mute / unmute the
line-out jacks per the headphone plug / unplug.  For achieving this
and keeping the compatibility with the old behavior, the new mixer
enum "Auto-Mute Mode" is added.  With this, user can control the
auto-mute behavior either disabled, speaker-only or lineout+speaker.
Signed-off-by: Takashi Iwai <tiwai@suse.de>