* Mediatek MT5896 SoC GPIO controller

The GPIO controller provides GPIO controls and interrupts.

Required properties for the top level node:
  - #gpio-cells : Should be two. The first cell is the GPIO pin number and the
      second cell specifies GPIO flags, as defined in <dt-bindings/gpio/gpio.h>.
      Only the GPIO_ACTIVE_HIGH and GPIO_ACTIVE_LOW flags are supported.
  - #interrupt-cells : Specifies the number of cells needed to encode an
      interrupt. Should be 2. The first cell defines the interrupt number,
      the second encodes the triger flags encoded as described in
      Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
  - compatible:
      - "mediatek,mt5896-gpio" for Mediatek controllers
  - reg : Physical base address and length of the controller's registers
  - interrupt-parent : phandle of the parent interrupt controller.
  - interrupts : Interrupt specifier for the controllers interrupt.
  - interrupt-controller : Mark the device node as an interrupt controller.
  - gpio-controller : Marks the device node as a GPIO controller.
  - ngpios: number of PADs in this GPIO controller.
  - base: the start index of this GPIO controller.
  - sub-index: the index in the register bank.

Example:
	gpio_pm_gpio0: gpio@1f001e00 {
		compatible = "mediatek,mt5896-gpio";
		reg = <0x0 0x1f001e00 0x0 0x200>;
		gpio-controller;
		#gpio-cells = <2>;
		ngpios = <28>;
		base = <4>;
		sub-index = <0>;
		interrupts = <0 55 0x4>;
	};
