dt-bindings: interrupt-controller: add Andes machine-level software interrupt controller

Add the DT binding documentation for Andes machine-level software
interrupt controller.

In the Andes platform such as QiLai SoC, the PLIC module is instantiated a
second time with all interrupt sources tied to zero as the software
interrupt controller (PLICSW). PLICSW can generate machine-level software
interrupts through programming its registers.

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Ben Zong-You Xie <ben717@andestech.com>
Link: https://lore.kernel.org/r/20250711133025.2192404-5-ben717@andestech.com
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Documentation/devicetree/bindings/interrupt-controller/andestech,plicsw.yaml

@@ -0,0 +1,54 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/interrupt-controller/andestech,plicsw.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Andes machine-level software interrupt controller
+
+description:
+  In the Andes platform such as QiLai SoC, the PLIC module is instantiated a
+  second time with all interrupt sources tied to zero as the software interrupt
+  controller (PLIC_SW). PLIC_SW directly connects to the machine-mode
+  inter-processor interrupt lines of CPUs, so RISC-V per-CPU local interrupt
+  controller is the parent interrupt controller for PLIC_SW. PLIC_SW can
+  generate machine-mode inter-processor interrupts through programming its
+  registers.
+
+maintainers:
+  - Ben Zong-You Xie <ben717@andestech.com>
+
+properties:
+  compatible:
+    items:
+      - enum:
+          - andestech,qilai-plicsw
+      - const: andestech,plicsw
+
+  reg:
+    maxItems: 1
+
+  interrupts-extended:
+    minItems: 1
+    maxItems: 15872
+    description:
+      Specifies which harts are connected to the PLIC_SW. Each item must points
+      to a riscv,cpu-intc node, which has a riscv cpu node as parent.
+
+additionalProperties: false
+
+required:
+  - compatible
+  - reg
+  - interrupts-extended
+
+examples:
+  - |
+    interrupt-controller@400000 {
+      compatible = "andestech,qilai-plicsw", "andestech,plicsw";
+      reg = <0x400000 0x400000>;
+      interrupts-extended = <&cpu0intc 3>,
+                            <&cpu1intc 3>,
+                            <&cpu2intc 3>,
+                            <&cpu3intc 3>;
+    };