ARM: S3C24XX: use samsung_sync_wakemask in s3c2412 pm

Originally the s3c2412 used a overidden irq chip to set the rtc wakeup flag.
But with using the samsung_sync_wakemask function the same can be achieved
without introducing soc specific irq functions.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>