watchdog: s3c2410: Use dev_dbg instead of pr_info

Replace the 'debug' module parameter and pr_info() with proper device
dynamic debug calls because this is the preferred and flexible way of
enabling debugging printks.

Also remove some obvious debug printks.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>