s3c64xx: Add ifdef at the S3C64XX only codes

The s3c6400.h file is only for S3C64XX cpu and the pheripheral port
address(0x70000000 - 0x7fffffff) exists at only S3C64XX cpu, so they
should be included by only S3C64XX cpu.

Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>