[ARM] 4156/1: S3C24XX: Add CONFIG_S3C2410_GPIO

In preperation for splitting the arch-s3c2410 directory
up, add a CONFIG_S3C2410_GPIO instead of implicitly
making the .o for CONFIG_CPU_S3C2410 and CONFIG_CPU_S3C2440

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