fbdev: display class

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 <jsimmons@infradead.org>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>