[PATCH] nvidiafb: Add boot option 'bpp'

Add boot/module option 'bpp' so user can specify at what color depth to boot
into.

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