[ARM] S3C24XX: Move files out of include/asm-arm/plat-s3c*

First move of items out of include/asm-arm/plat-s3c* to their
new homes under arch/arm/plat-s3c/include/plat and
arch/arm/plat-s3c24xx/include/plat directories.

Note, we have to create a dummy arch/arm/plat-s3c/Makefile to
allow us to add arch/arm/plat-s3c/include/plat to the path.

Signed-off-by: Ben Dooks <ben-linux@fluff.org>