Freescale IRQSTEER Interrupt multiplexer

Required properties:

- compatible: should be:
	- "fsl,imx8m-irqsteer"
	- "fsl,imx-irqsteer"
- reg: Physical base address and size of registers.
- interrupts: Should contain the parent interrupt line used to multiplex the
  input interrupts.
- clocks: Should contain one clock for entry in clock-names
  see Documentation/devicetree/bindings/clock/clock-bindings.txt
- clock-names:
   - "ipg": main logic clock
- interrupt-controller: Identifies the node as an interrupt controller.
- #interrupt-cells: Specifies the number of cells needed to encode an
  interrupt source. The value must be 1.
- fsl,channel: The output channel that all input IRQs should be steered into.
- fsl,irq-groups: Number of IRQ groups managed by this controller instance.
  Each group manages 64 input interrupts.

Example:

	interrupt-controller@32e2d000 {
		compatible = "fsl,imx8m-irqsteer", "fsl,imx-irqsteer";
		reg = <0x32e2d000 0x1000>;
		interrupts = <GIC_SPI 18 IRQ_TYPE_LEVEL_HIGH>;
		clocks = <&clk IMX8MQ_CLK_DISP_APB_ROOT>;
		clock-names = "ipg";
		fsl,channel = <0>;
		fsl,irq-groups = <1>;
		interrupt-controller;
		#interrupt-cells = <1>;
	};