dt-bindings: interrupt-controller: Add Loongson-3 HTPIC

Document Loongson-3 HyperTransport PIC controller.
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Co-developed-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

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

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: "http://devicetree.org/schemas/interrupt-controller/loongson,htpic.yaml#"
+$schema: "http://devicetree.org/meta-schemas/core.yaml#"
+
+title: Loongson-3 HyperTransport Interrupt Controller
+
+maintainers:
+  - Jiaxun Yang <jiaxun.yang@flygoat.com>
+
+allOf:
+  - $ref: /schemas/interrupt-controller.yaml#
+
+description: |
+  This interrupt controller is found in the Loongson-3 family of chips to transmit
+  interrupts from PCH PIC connected on HyperTransport bus.
+
+properties:
+  compatible:
+    const: loongson,htpic-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'
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/irq.h>
+    htintc: interrupt-controller@1fb000080 {
+      compatible = "loongson,htintc-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>;
+    };
+...