ARM: SAMSUNG: Add soc_is_s3c6400/s3c6410 macros

This patch adds soc_is_s3c6400() and soc_is_s3c6410() macros that allow
to distinguish between specific SoCs from s3c64xx series that is needed
to handle differences between them.

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>