ARM: SAMSUNG: Add soc_is_s3c2410() helper

Due to the S3C2410 SoC being quite different from other S3C24xx SoCs
in some aspects, such as availability of DIVSLOT register in its UART
blocks, there is a need sometimes to check whether we are running on
this SoC, not just the S3C24xx series. This patch adds soc_is_s3c2410()
helper function for this purpose.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>