watchdog: w83627hf_wdt: Support NCT6796D, NCT6797D, NCT6798D

The watchdog controller on NCT6796D, NCT6797D, and NCT6798D is compatible
with the wtachdog controller on other Nuvoton chips.

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