pinctrl: Broadcom NSP GPIO-a device tree bindings

Device tree binding documentation for Broadcom NSP GPIO-a
Signed-off-by: Yendapally Reddy Dhananjaya Reddy <yrdreddy@broadcom.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/pinctrl/brcm,nsp-gpio.txt

+Broadcom Northstar plus (NSP) GPIO/PINCONF Controller
+
+Required properties:
+- compatible:
+    Must be "brcm,nsp-gpio-a"
+
+- reg:
+    Should contain the register physical address and length for each of
+    GPIO base, IO control registers
+
+- #gpio-cells:
+    Must be two. The first cell is the GPIO pin number (within the
+    controller's pin space) and the second cell is used for the following:
+    bit[0]: polarity (0 for active high and 1 for active low)
+
+- gpio-controller:
+    Specifies that the node is a GPIO controller
+
+- ngpios:
+    Number of gpios supported (58x25 supports 32 and 58x23 supports 24)
+
+Optional properties:
+- interrupts:
+    Interrupt ID
+
+- interrupt-controller:
+    Specifies that the node is an interrupt controller
+
+- gpio-ranges:
+    Specifies the mapping between gpio controller and pin-controllers pins.
+    This requires 4 fields in cells defined as -
+    1. Phandle of pin-controller.
+    2. GPIO base pin offset.
+    3  Pin-control base pin offset.
+    4. number of gpio pins which are linearly mapped from pin base.
+
+Supported generic PINCONF properties in child nodes:
+- pins:
+    The list of pins (within the controller's own pin space) that properties
+    in the node apply to. Pin names are "gpio-<pin>"
+
+- bias-disable:
+    Disable pin bias
+
+- bias-pull-up:
+    Enable internal pull up resistor
+
+- bias-pull-down:
+    Enable internal pull down resistor
+
+- drive-strength:
+    Valid drive strength values include 2, 4, 6, 8, 10, 12, 14, 16 (mA)
+
+Example:
+
+	gpioa: gpio@18000020 {
+		compatible = "brcm,nsp-gpio-a";
+		reg = <0x18000020 0x100>,
+		      <0x1803f1c4 0x1c>;
+		#gpio-cells = <2>;
+		gpio-controller;
+		ngpios = <32>;
+		gpio-ranges = <&pinctrl 0 0 31>;
+		interrupt-controller;
+		interrupts = <GIC_SPI 85 IRQ_TYPE_LEVEL_HIGH>;
+
+		/* Hog a few default settings */
+		pinctrl-names = "default";
+		pinctrl-0 = <&led>;
+		led: led {
+			pins = "gpio-1";
+			bias-pull-up;
+		};
+
+		pwr: pwr {
+			gpio-hog;
+			gpios = <3 1>;
+			output-high;
+		};
+	};