Structure of irqchip.

Samples:

irq-bcm6345-l1.c:IRQCHIP_DECLARE(bcm6345_l1, "brcm,bcm6345-l1-intc", bcm6345_l1_of_init);
irq-bcm7038-l1.c:IRQCHIP_DECLARE(bcm7038_l1, "brcm,bcm7038-l1-intc", bcm7038_l1_of_init);
irq-bcm7120-l2.c:IRQCHIP_DECLARE(bcm7120_l2_intc, "brcm,bcm7120-l2-intc",
irq-bcm7120-l2.c:IRQCHIP_DECLARE(bcm3380_l2_intc, "brcm,bcm3380-l2-intc",
irq-brcmstb-l2.c:IRQCHIP_DECLARE(brcmstb_l2_intc, "brcm,l2-intc", brcmstb_l2_edge_intc_of_init);