watchdog: gpio: add support for nowayout option

Add support for the nowayout option in the gpio watchdog driver.

Signed-off-by: Mans Rullgard <mans@mansr.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>