[ARM] 3661/1: S3C2412: Fix compilation if CPU_S3C2410 only

Patch from Ben Dooks

If only the S3C2412 based machines are selected,
then the regs-dsc.h does not export the S3C2412_DSC
registers as it is wrapped in CONFIG_CPU_S3C2440.

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