gpio: add DT bindings for lpc1850-gpio driver

Signed-off-by: Joachim Eastwood <manabian@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/gpio/nxp,lpc1850-gpio.txt

+NXP LPC18xx/43xx GPIO controller Device Tree Bindings
+-----------------------------------------------------
+
+Required properties:
+- compatible		: Should be "nxp,lpc1850-gpio"
+- reg			: Address and length of the register set for the device
+- clocks		: Clock specifier (see clock bindings for details)
+- gpio-controller	: Marks the device node as a GPIO controller.
+- #gpio-cells 		: Should be two
+			  - First cell is the GPIO line number
+			  - Second cell is used to specify polarity
+
+Optional properties:
+- gpio-ranges		: Mapping between GPIO and pinctrl
+
+Example:
+#define LPC_GPIO(port, pin)	(port * 32 + pin)
+#define LPC_PIN(port, pin)	(0x##port * 32 + pin)
+
+gpio: gpio@400f4000 {
+	compatible = "nxp,lpc1850-gpio";
+	reg = <0x400f4000 0x4000>;
+	clocks = <&ccu1 CLK_CPU_GPIO>;
+	gpio-controller;
+	#gpio-cells = <2>;
+	gpio-ranges =	<&pinctrl LPC_GPIO(0,0)  LPC_PIN(0,0)  2>,
+			...
+			<&pinctrl LPC_GPIO(7,19) LPC_PIN(f,5)  7>;
+};
+
+gpio_joystick {
+	compatible = "gpio-keys-polled";
+	...
+
+	button@0 {
+		...
+		gpios = <&gpio LPC_GPIO(4,8) GPIO_ACTIVE_LOW>;
+	};
+};