Add backlight driver for Bachmann's ot200 visualisation device.  The
driver uses MFGPT 7 of CS5535 silicon to regulate the backlight.

[akpm@linux-foundation.org: remove redundant test of `brightness']
Signed-off-by: NChristian Gmeiner <christian.gmeiner@gmail.com>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: Andres Salomon <dilinger@queued.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>