dt-bindings: gpio: Add binding for Wii GPIO controller

The Nintendo Wii game console has a GPIO controller, which is used for
the optical disk slot LED, buttons, poweroff, etc. This patch adds a
binding for this GPIO controller.
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/gpio/nintendo,hollywood-gpio.txt

+Nintendo Wii (Hollywood) GPIO controller
+
+Required properties:
+- compatible: "nintendo,hollywood-gpio
+- reg: Physical base address and length of the controller's registers.
+- 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).
+
+Optional properties:
+- ngpios: see Documentation/devicetree/bindings/gpio/gpio.txt
+- interrupt-controller: Marks the device node as an interrupt controller.
+- #interrupt-cells: Should be two.
+- interrupts: Interrupt specifier for the controller's Broadway (PowerPC)
+  interrupt.
+- interrupt-parent: phandle of the parent interrupt controller.
+
+Example:
+
+	GPIO: gpio@d8000c0 {
+		#gpio-cells = <2>;
+		compatible = "nintendo,hollywood-gpio";
+		reg = <0x0d8000c0 0x40>;
+		gpio-controller;
+		ngpios = <24>;
+	}

Documentation/devicetree/bindings/powerpc/nintendo/wii.txt

@@ -152,14 +152,7 @@ Nintendo Wii device tree
 
 1.l) The General Purpose I/O (GPIO) controller node
 
-  Represents the dual access 32 GPIO controller interface.
-
-  Required properties:
-
-  - #gpio-cells : <2>
-  - compatible : should be "nintendo,hollywood-gpio"
-  - reg : should contain the IPC registers location and length
-  - gpio-controller
+  see Documentation/devicetree/bindings/gpio/nintendo,hollywood-gpio.txt
 
 1.m) The control node