ARM: SAMSUNG: Move WDT device definitions in plat-samsung

This patch moves the definitions of watchdog timer device from
plat-s3c24xx to plat-samsung. This will enable all Samsung S3C
and S5P series SoC's to use common WDT device definition.

Signed-off-by: Banajit Goswami <banajit.g@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Acked-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>