leds-ot200: Fix dependencies

The Bachmann OT200 is a Geode-based device, so OT200-specific drivers
are only useful on X86_32, except for build testing.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Bryan Wu <cooloney@gmail.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Bryan Wu <cooloney@gmail.com>