Broadcom BCM6345-style Level 1 interrupt controller

This block is a first level interrupt controller that is typically connected
directly to one of the HW INT lines on each CPU.

Key elements of the hardware design include:

- 32, 64 or 128 incoming level IRQ lines

- Most onchip peripherals are wired directly to an L1 input

- A separate instance of the register set for each CPU, allowing individual
  peripheral IRQs to be routed to any CPU

- Contains one or more enable/status word pairs per CPU

- No atomic set/clear operations

- No polarity/level/edge settings

- No FIFO or priority encoder logic; software is expected to read all
  2-4 status words to determine which IRQs are pending

Required properties:

- compatible: should be "brcm,bcm<soc>-l1-intc", "brcm,bcm6345-l1-intc"
- reg: specifies the base physical address and size of the registers;
  the number of supported IRQs is inferred from the size argument
- 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.
- interrupt-parent: specifies the phandle to the parent interrupt controller(s)
  this one is cascaded from
- interrupts: specifies the interrupt line(s) in the interrupt-parent controller
  node; valid values depend on the type of parent interrupt controller

If multiple reg ranges and interrupt-parent entries are present on an SMP
system, the driver will allow IRQ SMP affinity to be set up through the
/proc/irq/ interface.  In the simplest possible configuration, only one
reg range and one interrupt-parent is needed.

The driver operates in native CPU endian by default, there is no support for
specifying an alternative endianness.

Example:

periph_intc: interrupt-controller@10000000 {
        compatible = "brcm,bcm63168-l1-intc", "brcm,bcm6345-l1-intc";
        reg = <0x10000020 0x20>,
              <0x10000040 0x20>;

        interrupt-controller;
        #interrupt-cells = <1>;

        interrupt-parent = <&cpu_intc>;
        interrupts = <2>, <3>;
};