ARM: multi_v7_defconfig: Enable Samsung S3C SoC RTC

The rtc-s3c driver supports a range of S3C series Real-Time-Clocks found
on many Samsung SoCs. Build the driver as a module to support these RTC.

Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Kukjin Kim <kgene@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>