watchdog: it87_wdt: add IT8772 ID

IT8772 watchdog works as in IT872x

Tested on SHAREVDI K6-F12 board.

Signed-off-by: Hanspeter Portner <dev@open-music-kontrollers.ch>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20200827105940.2835910-1-hanspeter.portner@livesystems.ch


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