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>

arch/arm/Kconfig

@@ -689,7 +689,7 @@ config ARCH_S5P64X0
 	select HAVE_S3C2410_WATCHDOG if WATCHDOG
 	select ARCH_USES_GETTIMEOFFSET
 	select HAVE_S3C2410_I2C if I2C
-	select HAVE_S3C_RTC
+	select HAVE_S3C_RTC if RTC_CLASS
 	help
 	  Samsung S5P64X0 CPU based systems, such as the Samsung SMDK6440,
 	  SMDK6450.
@@ -712,7 +712,7 @@ config ARCH_S5PC100
 	select ARM_L1_CACHE_SHIFT_6
 	select ARCH_USES_GETTIMEOFFSET
 	select HAVE_S3C2410_I2C if I2C
-	select HAVE_S3C_RTC
+	select HAVE_S3C_RTC if RTC_CLASS
 	select HAVE_S3C2410_WATCHDOG if WATCHDOG
 	help
 	  Samsung S5PC100 series based systems
@@ -727,7 +727,7 @@ config ARCH_S5PV210
 	select ARCH_HAS_CPUFREQ
 	select ARCH_USES_GETTIMEOFFSET
 	select HAVE_S3C2410_I2C if I2C
-	select HAVE_S3C_RTC
+	select HAVE_S3C_RTC if RTC_CLASS
 	select HAVE_S3C2410_WATCHDOG if WATCHDOG
 	help
 	  Samsung S5PV210/S5PC110 series based systems
@@ -739,7 +739,7 @@ config ARCH_S5PV310
 	select GENERIC_GPIO
 	select HAVE_CLK
 	select GENERIC_CLOCKEVENTS
-	select HAVE_S3C_RTC
+	select HAVE_S3C_RTC if RTC_CLASS
 	select HAVE_S3C2410_I2C if I2C
 	select HAVE_S3C2410_WATCHDOG if WATCHDOG
 	help