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>

Documentation/devicetree/bindings/mips/cavium/ciu3.txt

@@ -0,0 +1,27 @@
+* Central Interrupt Unit v3
+
+Properties:
+- compatible: "cavium,octeon-7890-ciu3"
+
+  Compatibility with 78XX and 73XX SOCs.
+
+- interrupt-controller:  This is an interrupt controller.
+
+- reg: The base address of the CIU's register bank.
+
+- #interrupt-cells: Must be <2>.  The first cell is source number.
+  The second cell indicates the triggering semantics, and may have a
+  value of either 4 for level semantics, or 1 for edge semantics.
+
+Example:
+	interrupt-controller@1010000000000 {
+		compatible = "cavium,octeon-7890-ciu3";
+		interrupt-controller;
+		/* Interrupts are specified by two parts:
+		 * 1) Source number (20 significant bits)
+		 * 2) Trigger type: (4 == level, 1 == edge)
+		 */
+		#address-cells = <0>;
+		#interrupt-cells = <2>;
+		reg = <0x10100 0x00000000 0x0 0xb0000000>;
+	};