gpio: winbond: Add driver

This commit adds GPIO driver for Winbond Super I/Os.

Currently, only W83627UHG model (also known as Nuvoton NCT6627UD)
is supported but in the future a support for other Winbond models,
too, can be added to the driver.

A module parameter "gpios" sets a bitmask of GPIO ports to enable
(bit 0 is GPIO1, bit 1 is GPIO2, etc.).

One should be careful which ports one tinkers with since some
might be managed by the firmware (for functions like powering on and
off, sleeping, BIOS recovery, etc.) and some of GPIO port pins are
physically shared with other devices included in the Super I/O chip.

Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>