dt-bindings: serial: Convert socionext,milbeaut-usio-uart to DT schema

Convert the Socionext Milbeaut UART binding to DT schema. It is a
straight-forward conversion.

Reviewed-by: Thierry Reding <[e-mail]>
Signed-off-by: "Rob Herring (Arm)" <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/devicetree/bindings/serial/milbeaut-uart.txt

···
-Socionext Milbeaut UART controller
-
-Required properties:
-- compatible: should be "socionext,milbeaut-usio-uart".
-- reg: offset and length of the register set for the device.
-- interrupts: two interrupts specifier.
-- interrupt-names: should be "rx", "tx".
-- clocks: phandle to the input clock.
-
-Optional properties:
-- auto-flow-control: flow control enable.
-
-Example:
-	usio1: usio_uart@1e700010 {
-		compatible = "socionext,milbeaut-usio-uart";
-		reg = <0x1e700010 0x10>;
-		interrupts = <0 141 0x4>, <0 149 0x4>;
-		interrupt-names = "rx", "tx";
-		clocks = <&clk 2>;
-		auto-flow-control;
-	};

Documentation/devicetree/bindings/serial/socionext,milbeaut-usio-uart.yaml

···
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/serial/socionext,milbeaut-usio-uart.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Socionext Milbeaut UART controller
+
+maintainers:
+  - Sugaya Taichi <[e-mail]>
+
+allOf:
+  - $ref: /schemas/serial/serial.yaml#
+
+properties:
+  compatible:
+    const: socionext,milbeaut-usio-uart
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    items:
+      - description: RX interrupt specifier
+      - description: TX interrupt specifier
+
+  interrupt-names:
+    items:
+      - const: rx
+      - const: tx
+
+  clocks:
+    maxItems: 1
+
+  auto-flow-control:
+    description: Enable automatic flow control.
+    type: boolean
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - interrupt-names
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    serial@1e700010 {
+        compatible = "socionext,milbeaut-usio-uart";
+        reg = <0x1e700010 0x10>;
+        interrupts = <0 141 0x4>, <0 149 0x4>;
+        interrupt-names = "rx", "tx";
+        clocks = <&clk 2>;
+        auto-flow-control;
+    };