Add the new display class. This is meant to unite the various solutions to
display units ie acpi output device, auxdisplay and the defunct lcd class
in the backlight directory.

Signed-off-by: James Simmons
Cc: "Antonino A. Daplas"
Cc: Greg KH
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds