dt-bindings: serial: Convert sprd-uart to json-schema

Convert the sprd-uart binding to DT schema using json-schema.
Signed-off-by: Chunyan Zhang <chunyan.zhang@unisoc.com>
[robh: dual license GPL/BSD]
Signed-off-by: Rob Herring <robh@kernel.org>

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

-* Spreadtrum serial UART
-
-Required properties:
-- compatible: must be one of:
-  * "sprd,sc9836-uart"
-  * "sprd,sc9860-uart", "sprd,sc9836-uart"
-
-- reg: offset and length of the register set for the device
-- interrupts: exactly one interrupt specifier
-- clock-names: Should contain following entries:
-  "enable" for UART module enable clock,
-  "uart" for UART clock,
-  "source" for UART source (parent) clock.
-- clocks: Should contain a clock specifier for each entry in clock-names.
-  UART clock and source clock are optional properties, but enable clock
-  is required.
-
-Optional properties:
-- dma-names: Should contain "rx" for receive and "tx" for transmit channels.
-- dmas: A list of dma specifiers, one for each entry in dma-names.
-
-Example:
-	uart0: serial@0 {
-		compatible = "sprd,sc9860-uart",
-			     "sprd,sc9836-uart";
-		reg = <0x0 0x100>;
-		interrupts = <GIC_SPI 2 IRQ_TYPE_LEVEL_HIGH>;
-		dma-names = "rx", "tx";
-		dmas = <&ap_dma 19>, <&ap_dma 20>;
-		clock-names = "enable", "uart", "source";
-		clocks = <&clk_ap_apb_gates 9>, <&clk_uart0>, <&ext_26m>;
-	};

Documentation/devicetree/bindings/serial/sprd-uart.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+# Copyright 2019 Unisoc Inc.
+%YAML 1.2
+---
+$id: "http://devicetree.org/schemas/serial/sprd-uart.yaml#"
+$schema: "http://devicetree.org/meta-schemas/core.yaml#"
+
+title: Spreadtrum serial UART
+
+maintainers:
+  - Orson Zhai <orsonzhai@gmail.com>
+  - Baolin Wang <baolin.wang7@gmail.com>
+  - Chunyan Zhang <zhang.lyra@gmail.com>
+
+properties:
+  compatible:
+    oneOf:
+      - items:
+          - enum:
+              - sprd,sc9860-uart
+          - const: sprd,sc9836-uart
+      - const: sprd,sc9836-uart
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  clocks:
+    minItems: 1
+    maxItems: 3
+
+  clock-names:
+    description: |
+      "enable" for UART module enable clock, "uart" for UART clock, "source" 
+      for UART source (parent) clock.
+    items:
+      - const: enable
+      - const: uart
+      - const: source
+
+  dmas:
+    minItems: 1
+    maxItems: 2
+
+  dma-names:
+    minItems: 1
+    items:
+      - const: rx
+      - const: tx
+
+required:
+  - compatible
+  - reg
+  - interrupts
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+    serial@0 {
+      compatible = "sprd,sc9860-uart", "sprd,sc9836-uart";
+      reg = <0x0 0x100>;
+      interrupts = <GIC_SPI 2 IRQ_TYPE_LEVEL_HIGH>;
+      dma-names = "rx", "tx";
+      dmas = <&ap_dma 19>, <&ap_dma 20>;
+      clock-names = "enable", "uart", "source";
+      clocks = <&clk_ap_apb_gates 9>, <&clk_uart0>, <&ext_26m>;
+    };
+
+...