dt-bindings: interrupt-controller: Add Sophgo sg2042 CLINT mswi

The clint of Sophgo's sg2042 is based off IP designed by T-HEAD, and
implements the not yet frozen ACLINT spec. This spec seems to be
abandoned, and will not be frozen in the predictable future.
Frozen specs required by the RISC-V maintainers before merging content
relating to those extensions, therefore a generic compatible is not
appropriate.
Instead, add new vendor specific compatible strings to identify mswi of
sg2042 clint.
Signed-off-by: Inochi Amaoto <inochiama@outlook.com>
Signed-off-by: Chen Wang <unicorn_wang@outlook.com>
[conor: re-wrote commit message to drop irrelevant sifive,clint discussion]
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

Documentation/devicetree/bindings/interrupt-controller/thead,c900-aclint-mswi.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/interrupt-controller/thead,c900-aclint-mswi.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Sophgo sg2042 CLINT Machine-level Software Interrupt Device
+
+maintainers:
+  - Inochi Amaoto <inochiama@outlook.com>
+
+properties:
+  compatible:
+    items:
+      - enum:
+          - sophgo,sg2042-aclint-mswi
+      - const: thead,c900-aclint-mswi
+
+  reg:
+    maxItems: 1
+
+  interrupts-extended:
+    minItems: 1
+    maxItems: 4095
+
+additionalProperties: false
+
+required:
+  - compatible
+  - reg
+  - interrupts-extended
+
+examples:
+  - |
+    interrupt-controller@94000000 {
+      compatible = "sophgo,sg2042-aclint-mswi", "thead,c900-aclint-mswi";
+      interrupts-extended = <&cpu1intc 3>,
+                            <&cpu2intc 3>,
+                            <&cpu3intc 3>,
+                            <&cpu4intc 3>;
+      reg = <0x94000000 0x00010000>;
+    };
+...