watchdog: Add Advantech EC watchdog driver

This patch adds the 'advantech_ec_wdt' kernel module which provides
WDT support for Advantech platforms with ITE based Embedded Controller.

Signed-off-by: Thomas Kastner <thomas.kastner@advantech.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Thomas Kastner <thomas.kastner@advantech.com>
Link: https://lore.kernel.org/r/Y0+pl/26e3pcEUPk@EIS-S230
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>