gpio: it87: add support for IT8718F Super I/O.

The DIO connector on the WAFER-945GSE is interfaced to GPIO ports
on the ITE IT8718F Super I/O chipset. From the datasheet of ITE IT8718F,
the GPIO interface is identical to IT8728, so just add it
to the same case as the other chip.

Signed-off-by: Ivan Podovalov <ipodovalov@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>