gpio: add GPIO support for F71882FG and F71889F

This patch adds support for the GPIOs found on the Fintek super-I/O
chips F71882FG and F71889F.

A super-I/O is a legacy I/O controller embedded on x86 motherboards. It
is used to connect the low-bandwidth devices. Among others functions the
F71882FG/F71889F provides: a parallel port, two serial ports, a keyboard
controller, an hardware monitoring controller and some GPIO pins.

Note that this super-I/Os are embedded on some Atom-based LaCie NASes.
The GPIOs are used to control the LEDs and the hard drive power.

Changes since v3:
- Use request_muxed_region to protect the I/O ports against concurrent
  accesses.

Changes since v2:
- Remove useless NULL setters for driver data.

Changes since v1:
- Enhance the commit message by describing what is a Super-I/O.
- Use self-explanatory names for the GPIO register macros.
- Add a comment to explain the platform device and driver registration.
- Fix gpio_get when GPIO is configured in input mode. I only had
  the hardware to check this mode recently...

Signed-off-by: Simon Guinot <simon.guinot@sequanux.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index 156fd28..97438bf 100644
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -24,6 +24,7 @@
 obj-$(CONFIG_ARCH_DAVINCI)	+= gpio-davinci.o
 obj-$(CONFIG_GPIO_EM)		+= gpio-em.o
 obj-$(CONFIG_GPIO_EP93XX)	+= gpio-ep93xx.o
+obj-$(CONFIG_GPIO_F7188X)	+= gpio-f7188x.o
 obj-$(CONFIG_GPIO_GE_FPGA)	+= gpio-ge.o
 obj-$(CONFIG_GPIO_GRGPIO)	+= gpio-grgpio.o
 obj-$(CONFIG_GPIO_ICH)		+= gpio-ich.o