gpio: add TB10x GPIO driver

The GPIO driver for the Abilis Systems TB10x series of SOCs based on ARC700
CPUs. It supports GPIO control and GPIO interrupt generation. This driver
works in conjunction with the TB10x pinctrl driver.

Signed-off-by: Sascha Leuenberger <sascha.leuenberger@abilis.com>
Signed-off-by: Christian Ruppert <christian.ruppert@abilis.com>
Acked-by: Kumar Gala <galak@codeaurora.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/gpio/abilis,tb10x-gpio.txt

@@ -0,0 +1,36 @@
+* Abilis TB10x GPIO controller
+
+Required Properties:
+- compatible: Should be "abilis,tb10x-gpio"
+- reg: Address and length of the register set for the device
+- gpio-controller: Marks the device node as a gpio controller.
+- #gpio-cells: Should be <2>. The first cell is the pin number and the
+  second cell is used to specify optional parameters:
+   - bit 0 specifies polarity (0 for normal, 1 for inverted).
+- abilis,ngpio: the number of GPIO pins this driver controls.
+
+Optional Properties:
+- interrupt-controller: Marks the device node as an interrupt controller.
+- #interrupt-cells: Should be <1>. Interrupts are triggered on both edges.
+- interrupts: Defines the interrupt line connecting this GPIO controller to
+  its parent interrupt controller.
+- interrupt-parent: Defines the parent interrupt controller.
+
+GPIO ranges are specified as described in
+Documentation/devicetree/bindings/gpio/gpio.txt
+
+Example:
+
+	gpioa: gpio@FF140000 {
+		compatible = "abilis,tb10x-gpio";
+		interrupt-controller;
+		#interrupt-cells = <1>;
+		interrupt-parent = <&tb10x_ictl>;
+		interrupts = <27 2>;
+		reg = <0xFF140000 0x1000>;
+		gpio-controller;
+		#gpio-cells = <2>;
+		abilis,ngpio = <3>;
+		gpio-ranges = <&iomux 0 0 0>;
+		gpio-ranges-group-names = "gpioa_pins";
+	};