ZTE ZX296702 GPIO controller

Required properties:
- compatible : "zte,zx296702-gpio"
- #gpio-cells : Should be two. 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)
- gpio-controller : Marks the device node as a GPIO controller.
- interrupts : Interrupt mapping for GPIO IRQ.
- gpio-ranges : Interaction with the PINCTRL subsystem.

gpio1: gpio@b008040 {
	compatible = "zte,zx296702-gpio";
	reg = <0xb008040 0x40>;
	gpio-controller;
	#gpio-cells = <2>;
	gpio-ranges = < &pmx0 0 54 2 &pmx0 2 59 14>;
	interrupts = <GIC_SPI 26 IRQ_TYPE_LEVEL_HIGH>;
	interrupt-parent = <&intc>;
	interrupt-controller;
	#interrupt-cells = <2>;
	clock-names = "gpio_pclk";
	clocks = <&lsp0clk ZX296702_GPIO_CLK>;
};

Document ZTE zx296702 GPIO DT binding
gpio: Document ZTE zx296702 GPIO DT binding

Add document of ZTE zx296702 GPIO binding

Signed-off-by: Jun Nie <16d8bc3f29c489fdc436b48884adedee8c6f9a7b@linaro.org>
Acked-by: Shawn Guo <912cf7eb7d8018e2943586ae6657d21fd4e38239@linaro.org>
Signed-off-by: Linus Walleij <9cd9d802d23c0ed5e224beabf4ae4a5c478746ef@linaro.org>
