MIPS: OCTEON: Add support for OCTEON III interrupt controller.

Add irq_chip support for both IPI and "normal" interrupts of the CIU3
controller.  Document the device tree binding for the CIU3.

Some functions are non-static as they will be used by follow-on
support for MSI-X.

Signed-off-by: David Daney <david.daney@cavium.com>
Acked-by: Rob Herring <robh@kernel.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>
Cc: devicetree@vger.kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12500/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>