ARM: SAMSUNG: Move RTC device definitions in plat-samsung

This patch moves RTC device definitions from mach-s3c64xx
to plat-samsung, to enable the other SoCs to use same device
definition.

Signed-off-by: Atul Dahiya <atul.dahiya@samsung.com>
Signed-off-by: Sangbeom Kim <sbkim73@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>