watchdog: it87_wdt: add IT8786 ID

IT8786 watchdog works as in IT872x

Tested on VECOW ECS-9000 board.

Signed-off-by: Vincent Prince <Vincent.PRINCE.fr@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20200123140544.25937-1-vincent.prince.fr@gmail.com


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