Spreadtrum ipa level2 interrupt controller

This interrupt controller is only used on roc1 chip. It has the
following properties:

- outputs a single interrupt signal to its interrupts controller parent(GIC).

Required properties:

- compatible: should be "sprd,ud710-ipa-intc"
- reg: specifies the register base physical address and length
- interrupt-controller: identifies the node as an interrupt controller
- #interrupt-cells: specifies the number of cells needed to encode an interrupt
		    source, should be 1.
		    It specifies the interrupt number in this controller.
- interrupts: specifies the interrupt line in the interrupt-parent controller
	      (GIC) node
- syscons: The global registers of ipa interrupt controller.
	   Each group syscon has 3 cells.
- syscon-name: each mask of global register needs a corresponding name.

Example:

ipa_intc: ipa@20e03000 {
	compatible = "sprd,ud710-ipa-intc";
	reg = <0 0x20e03000 0 0x1000>;
	interrupt-controller;
	interrupts = <GIC_SPI 146 IRQ_TYPE_LEVEL_HIGH>;
	#interrupt-cells = <1>;
	syscon-names =  "ipa_intc_eb";
	syscons = <&ipa_ahb_regs REG_IPA_AHB_IPA_EB MASK_IPA_AHB_INTC_EB>;
};

