dt-bindings: interrupt-controller: Add Loongson HTVEC

Add binding for Loongson-3 HyperTransport Interrupt Vector Controller.
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200528152757.1028711-3-jiaxun.yang@flygoat.com

Documentation/devicetree/bindings/interrupt-controller/loongson,htvec.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: "http://devicetree.org/schemas/interrupt-controller/loongson,htvec.yaml#"
+$schema: "http://devicetree.org/meta-schemas/core.yaml#"
+
+title: Loongson-3 HyperTransport Interrupt Vector Controller
+
+maintainers:
+  - Jiaxun Yang <jiaxun.yang@flygoat.com>
+
+description:
+  This interrupt controller is found in the Loongson-3 family of chips for
+  receiving vectorized interrupts from PCH's interrupt controller.
+
+properties:
+  compatible:
+    const: loongson,htvec-1.0
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    minItems: 1
+    maxItems: 4
+    description: Four parent interrupts that receive chained interrupts.
+
+  interrupt-controller: true
+
+  '#interrupt-cells':
+    const: 1
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - interrupt-controller
+  - '#interrupt-cells'
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/irq.h>
+    htvec: interrupt-controller@fb000080 {
+      compatible = "loongson,htvec-1.0";
+      reg = <0xfb000080 0x40>;
+      interrupt-controller;
+      #interrupt-cells = <1>;
+
+      interrupt-parent = <&liointc>;
+      interrupts = <24 IRQ_TYPE_LEVEL_HIGH>,
+                    <25 IRQ_TYPE_LEVEL_HIGH>,
+                    <26 IRQ_TYPE_LEVEL_HIGH>,
+                    <27 IRQ_TYPE_LEVEL_HIGH>;
+    };
+...