gpio: add support for the Diolan DLN-2 USB GPIO driver

This patch adds GPIO and IRQ support for the Diolan DLN-2 GPIO module.

Information about the USB protocol interface can be found in the
Programmer's Reference Manual [1], see section 2.9 for the GPIO
module commands and responses.

[1] https://www.diolan.com/downloads/dln-api-manual.pdf

Signed-off-by: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Octavian Purdila <octavian.purdila@intel.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/gpio/Kconfig

@@ -905,4 +905,16 @@ config GPIO_VIPERBOARD
           River Tech's viperboard.h for detailed meaning
           of the module parameters.
 
+config GPIO_DLN2
+	tristate "Diolan DLN2 GPIO support"
+	depends on MFD_DLN2
+	select GPIOLIB_IRQCHIP
+
+	help
+	  Select this option to enable GPIO driver for the Diolan DLN2
+	  board.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called gpio-dln2.
+
 endif

drivers/gpio/Makefile

@@ -26,6 +26,7 @@ obj-$(CONFIG_GPIO_CRYSTAL_COVE)	+= gpio-crystalcove.o
 obj-$(CONFIG_GPIO_DA9052)	+= gpio-da9052.o
 obj-$(CONFIG_GPIO_DA9055)	+= gpio-da9055.o
 obj-$(CONFIG_GPIO_DAVINCI)	+= gpio-davinci.o
+obj-$(CONFIG_GPIO_DLN2)		+= gpio-dln2.o
 obj-$(CONFIG_GPIO_DWAPB)	+= gpio-dwapb.o
 obj-$(CONFIG_GPIO_EM)		+= gpio-em.o
 obj-$(CONFIG_GPIO_EP93XX)	+= gpio-ep93xx.o