watchdog: it87_wdt: add IT8784 ID

IT8784 watchdog works as in IT878x

Tested on SHAREVDY K10 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/20200904211639.18787-2-dev@open-music-kontrollers.ch


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