ARM: S3C24XX: move plat-samsung/s3c24XX headers to local common.h

The different soc functions are now only used in the mach-s3c24xx
directory, so it's not necessary anymore to keep the globally
visible.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>