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>

drivers/gpio/Kconfig

@@ -146,6 +146,16 @@ config GPIO_MM_LANTIQ
 	  (EBU) found on Lantiq SoCs. The gpios are output only as they are
 	  created by attaching a 16bit latch to the bus.
 
+config GPIO_F7188X
+	tristate "F71882FG and F71889F GPIO support"
+	depends on X86
+	help
+	  This option enables support for GPIOs found on Fintek Super-I/O
+	  chips F71882FG and F71889F.
+
+	  To compile this driver as a module, choose M here: the module will
+	  be called f7188x-gpio.
+
 config GPIO_MPC5200
 	def_bool y
 	depends on PPC_MPC52xx

drivers/gpio/Makefile

@@ -24,6 +24,7 @@ obj-$(CONFIG_GPIO_DA9055)	+= gpio-da9055.o
 obj-$(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