dt-bindings: gpio: Add bindings for Cadence GPIO

This patch adds a DT binding documentation for
Cadence GPIO controller.
Signed-off-by: Jan Kotas <jank@cadence.com>
Reviewed-by: Rob Herring <robh@kernel.org>
[Removed interrupt-parent]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/gpio/cdns,gpio.txt

+Cadence GPIO controller bindings
+
+Required properties:
+- compatible: should be "cdns,gpio-r1p02".
+- reg: the register base address and size.
+- #gpio-cells: should be 2.
+	* first cell is the GPIO number.
+	* second cell specifies the GPIO flags, as defined in
+		<dt-bindings/gpio/gpio.h>. Only the GPIO_ACTIVE_HIGH
+		and GPIO_ACTIVE_LOW flags are supported.
+- gpio-controller: marks the device as a GPIO controller.
+- clocks: should contain one entry referencing the peripheral clock driving
+	the GPIO controller.
+
+Optional properties:
+- ngpios: integer number of gpio lines supported by this controller, up to 32.
+- interrupts: interrupt specifier for the controllers interrupt.
+- interrupt-controller: marks the device as an interrupt controller. When
+	defined, interrupts, interrupt-parent and #interrupt-cells
+	are required.
+- interrupt-cells: should be 2.
+	* first cell is the GPIO number you want to use as an IRQ source.
+	* second cell specifies the IRQ type, as defined in
+		<dt-bindings/interrupt-controller/irq.h>.
+		Currently only level sensitive IRQs are supported.
+
+
+Example:
+	gpio0: gpio-controller@fd060000 {
+		compatible = "cdns,gpio-r1p02";
+		reg =<0xfd060000 0x1000>;
+
+		clocks = <&gpio_clk>;
+
+		interrupt-parent = <&gic>;
+		interrupts = <0 5 IRQ_TYPE_LEVEL_HIGH>;
+
+		gpio-controller;
+		#gpio-cells = <2>;
+
+		interrupt-controller;
+		#interrupt-cells = <2>;
+	};