ARM: SAMSUNG: Save UART DIVSLOT register based on SoC type

The only SoC that does not have DIVSLOT register is S3C2410, so instead
of exporting a variable for platforms to set if DIVSLOT register should
be preserved, it's enough to simply check whether we are running on
a S3C2410 instead.

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>