rtc: ds1374: wdt: Use watchdog core for watchdog part

Let ds1374 watchdog use watchdog core functions. It also includes
improving watchdog timer setting and nowayout, and just uses ioctl()
of watchdog core.

Signed-off-by: Johnson Chen <johnsonch.chen@moxa.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/HK2PR01MB328182D5A54BFAA8A22E448AFA640@HK2PR01MB3281.apcprd01.prod.exchangelabs.com