gpio: f7188x: add GPIO support for F71869

Add support for the GPIOs found on the Fintek SuperI/O chip F71869, such
as the one found on the Jetway NF96u-525 motherboard, to the f7188x gpio
driver.

Signed-off-by: Andreas Bofjall <andreas@gazonk.org>
Tested-by: Les Schaffer <schaffer@optonline.net>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>