watchdog: s3c2410_wdt - Add extra option to include watchdog for Samsung SoCs

This patch adds HAVE_S3C2410_WATCHDOG to control inclusion of watchdog driver
for Samsung SoCs. This option will help to include the driver only for the
necessary machines and not for all for any given arch.

Signed-off-by: Banajit Goswami <banajit.g@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>