dt-bindings: Document Loongson RS780E PCH ACPI Controller

This controller is attached under ISA Bus and can be found
in Loongson-3 systems with RS780E PCH.
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

Documentation/devicetree/bindings/mips/loongson/rs780e-acpi.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: "http://devicetree.org/schemas/mips/loongson/rs780e-acpi.yaml#"
+$schema: "http://devicetree.org/meta-schemas/core.yaml#"
+
+title: Loongson RS780E PCH ACPI Controller
+
+maintainers:
+  - Jiaxun Yang <jiaxun.yang@flygoat.com>
+
+description: |
+  This controller can be found in Loongson-3 systems with RS780E PCH.
+
+properties:
+  compatible:
+    const: loongson,rs780e-acpi
+
+  reg:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+
+examples:
+  - |
+    isa@0 {
+      compatible = "isa";
+      #address-cells = <2>;
+      #size-cells = <1>;
+      ranges = <1 0 0 0x1000>;
+
+      acpi@800 {
+        compatible = "loongson,rs780e-acpi";
+        reg = <1 0x800 0x100>;
+      };
+    };
+
+...