Add Dock USB Audio Support for Samsung Car / Desk Docks

Ported from CM10, original patch: http://review.cyanogenmod.com/20586

Also includes patches:
DockAudio: Always route audio back to normal on undock.
http://review.cyanogenmod.org/24830

Bugfix: Dock events can have state greater than 1
http://review.cyanogenmod.org/24995

------------------------------------------------------

Samsung docks have a non-sensing USB adio port.
Samsung get around this by having a separate Setting to route the Audio
The Changes made will only add the extra Observer if the Kernel supports the endpoint

  /sys/class/switch/dock/state

Change-Id: I8e8f5001d5c651b07bb6af496bbf806732be21fa