Keystone 2 IRQ controller IP

On Keystone SOCs, DSP cores can send interrupts to ARM
host using the IRQ controller IP. It provides 28 IRQ signals to ARM.
The IRQ handler running on HOST OS can identify DSP signal source by
analyzing SRCCx bits in IPCARx registers. This is one of the component
used by the IPC mechanism used on Keystone SOCs.

Required Properties:
- compatible: should be "ti,keystone-irq"
- ti,syscon-dev : phandle and offset pair. The phandle to syscon used to
			access device control registers and the offset inside
			device control registers range.
- interrupt-controller : Identifies the node as an interrupt controller
- #interrupt-cells : Specifies the number of cells needed to encode interrupt
					 source should be 1.
- interrupts: interrupt reference to primary interrupt controller

Please refer to interrupts.txt in this directory for details of the common
Interrupt Controllers bindings used by client devices.

Example:
	kirq0: keystone_irq0@26202a0 {
		compatible = "ti,keystone-irq";
		ti,syscon-dev = <&devctrl 0x2a0>;
		interrupts = <GIC_SPI 4 IRQ_TYPE_EDGE_RISING>;
		interrupt-controller;
		#interrupt-cells = <1>;
	};

	dsp0: dsp0 {
		compatible = "linux,rproc-user";
		...
		interrupt-parent = <&kirq0>;
		interrupts = <10 2>;
	};
