output: Add display output class support

Add generic abstract layer for display output switch control.  The output
sysfs class driver provides an abstract video output layer that can be used to
hook platform specific methods to enable/disable video output device through
common sysfs interface.

Signed-off-by: Luming Yu <Luming.yu@intel.com>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Len Brown <len.brown@intel.com>