The Kconfig help text doesnt mention that in order to load the vfb module, you
have to pass in the parameter vfb_enable=1

Document required module options in Kconfig for loading the vfb module.
Signed-off-by: NAntonino Daplas <adaplas@pol.net>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>