[ARM] 4218/1: S3C2412: fix CONFIG_CPU_S3C2412_ONLY wrt to S3C2443

Update the Kconfig of arch/arm/mach-s3c2443 to
add the CONFIG_CPU_S3C2443 to the list of config
variabls which mean CONFIG_CPU_S3C2412_ONLY cannot
be set

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>