watchdog: s3c2410: Add support for device tree based probe

This patch adds the of_match_table to enable s3c2410-wdt driver
to be probed when watchdog device node is found in the device tree.

Signed-off-by: Thomas Abraham <thomas.abraham@linaro.org>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>