dt-bindings: serial: Convert cnxt,cx92755-usart to DT schema

Convert the Conexant Digicolor USART binding to DT schema. It is a
straight-forward conversion.

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

Documentation/devicetree/bindings/serial/cnxt,cx92755-usart.yaml

···
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/serial/cnxt,cx92755-usart.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Conexant Digicolor USART
+
+maintainers:
+  - Baruch Siach <[e-mail]>
+
+description: >
+  Note: this binding is only applicable for using the USART peripheral as UART.
+  USART also support synchronous serial protocols like SPI and I2S.
+  Use the binding that matches the wiring of your system.
+
+allOf:
+  - $ref: /schemas/serial/serial.yaml#
+
+properties:
+  compatible:
+    const: cnxt,cx92755-usart
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - interrupts
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    serial@f0000740 {
+        compatible = "cnxt,cx92755-usart";
+        reg = <0xf0000740 0x20>;
+        clocks = <&main_clk>;
+        interrupts = <44>;
+    };

Documentation/devicetree/bindings/serial/digicolor-usart.txt

···
-Binding for Conexant Digicolor USART
-
-Note: this binding is only applicable for using the USART peripheral as
-UART. USART also support synchronous serial protocols like SPI and I2S. Use
-the binding that matches the wiring of your system.
-
-Required properties:
-- compatible : should be "cnxt,cx92755-usart".
-- reg: Should contain USART controller registers location and length.
-- interrupts: Should contain a single USART controller interrupt.
-- clocks: Must contain phandles to the USART clock
-  See ../clocks/clock-bindings.txt for details.
-
-Note: Each UART port should have an alias correctly numbered
-in "aliases" node.
-
-Example:
-	aliases {
-		serial0 = &uart0;
-	};
-
-	uart0: uart@f0000740 {
-		compatible = "cnxt,cx92755-usart";
-		reg = <0xf0000740 0x20>;
-		clocks = <&main_clk>;
-		interrupts = <44>;
-	};