ARM: SAMSUNG: Make RTC driver dependency SoC specific instead of machine specific

This patch moves the dependency of RTC driver from MACH_XXX(board) to
ARCH_XXX(SoC). This will enable all machines using Samsung S5P6440, S5PC100
and S5PV210 SoCs to use RTC driver by default.

Signed-off-by: Atul Dahiya <atul.dahiya@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>