dt-bindings: MIPS: Document Ingenic SoCs binding.

Document the available properties for the SoC root node and the
CPU nodes of the devicetree for the Ingenic XBurst SoCs.
Tested-by: H. Nikolaus Schaller <hns@goldelico.com>
Tested-by: Paul Boddie <paul@boddie.org.uk>
Signed-off-by: 周琰杰 (Zhou Yanjie) <zhouyanjie@wanyeetech.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

Documentation/devicetree/bindings/mips/ingenic/ingenic,cpu.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mips/ingenic/ingenic,cpu.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Bindings for Ingenic XBurst family CPUs
+
+maintainers:
+  - 周琰杰 (Zhou Yanjie) <zhouyanjie@wanyeetech.com>
+
+description:
+  Ingenic XBurst family CPUs shall have the following properties.
+
+properties:
+  compatible:
+    oneOf:
+
+      - description: Ingenic XBurst®1 CPU Cores
+        enum:
+          - ingenic,xburst-mxu1.0
+          - ingenic,xburst-fpu1.0-mxu1.1
+          - ingenic,xburst-fpu2.0-mxu2.0
+
+      - description: Ingenic XBurst®2 CPU Cores
+        enum:
+          - ingenic,xburst2-fpu2.1-mxu2.1-smt
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+required:
+  - device_type
+  - compatible
+  - reg
+  - clocks
+
+examples:
+  - |
+    #include <dt-bindings/clock/jz4780-cgu.h>
+
+    cpus {
+	#address-cells = <1>;
+	#size-cells = <0>;
+
+	cpu0: cpu@0 {
+		device_type = "cpu";
+		compatible = "ingenic,xburst-fpu1.0-mxu1.1";
+		reg = <0>;
+
+		clocks = <&cgu JZ4780_CLK_CPU>;
+		clock-names = "cpu";
+	};
+
+	cpu1: cpu@1 {
+		device_type = "cpu";
+		compatible = "ingenic,xburst-fpu1.0-mxu1.1";
+		reg = <1>;
+
+		clocks = <&cgu JZ4780_CLK_CORE1>;
+		clock-names = "cpu";
+	};
+    };
+...