KEYMILE bfticu Chassis Management FPGA

The bfticu is a multifunction device that manages the whole chassis.
Its main functionality is to collect IRQs from the whole chassis and signals
them to a single controller.

Required properties:
- compatible: "keymile,bfticu"
- interrupt-controller: the bfticu FPGA is an interrupt controller
- interrupts: the main IRQ line to signal the collected IRQs
- #interrupt-cells : is 2 and their usage is compliant to the 2 cells variant
  of Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
- reg: access on the parent local bus (chip select, offset in chip select, size)

Example:

	chassis-mgmt@3,0 {
		compatible = "keymile,bfticu";
		interrupt-controller;
		#interrupt-cells = <2>;
		reg = <3 0 0x100>;
		interrupt-parent = <&mpic>;
		interrupts = <6 1 0 0>;
	};
