[PATCH] backlight: Fix Kconfig dependency

CONFIG_FB = m and CONFIG_{BACKLIGHT:LCD}_CLASS_DEVICE = y is possible
resulting in link errors.  Fix by making backlight and lcd class also depend
on FB

Signed-off-by: Antonino Daplas <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>