mfd: Fix cs5535 dependencies

As far as I know, the CS5535 and CS5536 chipsets are companions of the
Geode series of processors, which are 32-bit only. So the CS5535
drivers are not needed on x86-64, except for build testing purpose.

This aligns the dependencies to what FB_GEODE already uses.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>