ARM: odroidxu3_defconfig: disable CONFIG_RTC_DRV_S3C

ARM: odroidxu3_defconfig: disable CONFIG_RTC_DRV_S3C

Odroid-XU3 board has two rtc devices - SoC rtc(rtc-s3c) and pmic rtc
(rtc-s5m), so two device nodes for rtc like /dev/rtc0 and /dev/rtc1 will
be created.

The pmic rtc can keep time via rtc backup battery, so tizen platform
will want to use pmic rtc than SoC rtc but it can't know which device
node is for pmic rtc.

This patch disables CONFIG_RTC_DRV_S3C, then tizen platform can use only
pmic rtc.

Change-Id: Ie4256d547c9263c6bcb0302aacd7fbd3b47a4048
Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>