watchdog: ziirave: Use watchdog infrastructure to create sysfs attributes

The watchdog core now supports creating driver specific sysfs attributes
when creating the watchdog device.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>