ARM: SAMSUNG: Fix HAVE_S3C_RTC warnings

This patch fixes followng build warnings.
warning: (ARCH_S5P64X0 && <choice> || ARCH_S5PC100 && <choice> ||
          ARCH_S5PV210 && <choice> || ARCH_S5PV310 && <choice>)
         selects HAVE_S3C_RTC which has unmet direct dependencies (RTC_CLASS)

Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>