rtc: rtc-s3c: Updates RTC driver for clock enabling support

This Patch updates existing Samsung RTC driver for clock enabling support.

Signed-off-by: Atul Dahiya <atul.dahiya@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Cc: Ben Dooks <ben-linux@fluff.org>
Acked-by: Wan ZongShun <mcuos.com@gmail.com>