dt-bindings: interrupt-controller: Andestech Internal Vector Interrupt Controller

This patch adds an irqchip driver document for the Andestech Internal Vector
Interrupt Controller.
Signed-off-by: Rick Chen <rick@andestech.com>
Signed-off-by: Greentime Hu <greentime@andestech.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>

Documentation/devicetree/bindings/interrupt-controller/andestech,ativic32.txt

+* Andestech Internal Vector Interrupt Controller
+
+The Internal Vector Interrupt Controller (IVIC) is a basic interrupt controller
+suitable for a simpler SoC platform not requiring a more sophisticated and
+bigger External Vector Interrupt Controller.
+
+
+Main node required properties:
+
+- compatible : should at least contain  "andestech,ativic32".
+- interrupt-controller : Identifies the node as an interrupt controller
+- #interrupt-cells: 1 cells and refer to interrupt-controller/interrupts
+
+Examples:
+	intc: interrupt-controller {
+		compatible = "andestech,ativic32";
+		#interrupt-cells = <1>;
+		interrupt-controller;
+	};