FB: sa1100: combine RGB bitfield overrides into sa1100fb_mach_info

Allow the sa1100fb_mach_info structure to carry the RGB bitfield
overrides, rather than requiring them to be separately initialized
in sa1100fb_get_machine_info().

Acked-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>