dt-bindings: serial: brcm,bcm6345-uart: convert to the json-schema

This helps validating DTS files.

Redundant generic descriptions (e.g. "The base address of the UART
register bank") were dropped and periph_clk was dropped from example as
not required.

Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Link: https://lore.kernel.org/r/20210829131927.13682-1-zajec5@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/brcm,bcm6345-uart.yaml

@@ -0,0 +1,47 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/serial/brcm,bcm6345-uart.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: BCM63xx UART
+
+maintainers:
+  - Rafał Miłecki <rafal@milecki.pl>
+
+allOf:
+  - $ref: serial.yaml#
+
+properties:
+  compatible:
+    const: brcm,bcm6345-uart
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+  clock-names:
+    const: refclk
+
+unevaluatedProperties: false
+
+required:
+  - reg
+  - interrupts
+  - clocks
+
+examples:
+  - |
+    serial@14e00520 {
+        compatible = "brcm,bcm6345-uart";
+        reg = <0x14e00520 0x18>;
+        interrupt-parent = <&periph_intc>;
+        interrupts = <2>;
+        clocks = <&periph_clk>;
+        clock-names = "refclk";
+    };