ARM: S3C24XX: Remove plat-s3c24xx directory in arch/arm/

This patch is for just moving plat-s3c24xx/*.c into mach-s3c24xx/, so
that we could remove plat-s3c24xx directory. But since the PLAT_S3C24XX
is used in drivers, the statement is not deleted and it will be sorted
out next time.

Cc: Ben Dooks <ben-linux@fluff.org>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>