dt-bindings: mvebu-uart: document DT bindings for marvell,armada-3700-uart-clock

Add DT bindings documentation for device nodes with compatible string
"marvell,armada-3700-uart-clock".
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Marek Behún <kabel@kernel.org>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Marek Behún <kabel@kernel.org>
Link: https://lore.kernel.org/r/20220219152818.4319-3-kabel@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/clock/marvell,armada-3700-uart-clock.yaml

+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/clock/marvell,armada-3700-uart-clock.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+title: Marvell Armada 3720 UART clocks
+
+maintainers:
+  - Pali Rohár <pali@kernel.org>
+
+properties:
+  compatible:
+    const: marvell,armada-3700-uart-clock
+
+  reg:
+    items:
+      - description: UART Clock Control Register
+      - description: UART 2 Baud Rate Divisor Register
+
+  clocks:
+    description: |
+      List of parent clocks suitable for UART from following set:
+        "TBG-A-P", "TBG-B-P", "TBG-A-S", "TBG-B-S", "xtal"
+      UART clock can use one from this set and when more are provided
+      then kernel would choose and configure the most suitable one.
+      It is suggest to specify at least one TBG clock to achieve
+      baudrates above 230400 and also to specify clock which bootloader
+      used for UART (most probably xtal) for smooth boot log on UART.
+
+  clock-names:
+    items:
+      - const: TBG-A-P
+      - const: TBG-B-P
+      - const: TBG-A-S
+      - const: TBG-B-S
+      - const: xtal
+    minItems: 1
+
+  '#clock-cells':
+    const: 1
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - clock-names
+  - '#clock-cells'
+
+additionalProperties: false
+
+examples:
+  - |
+    uartclk: clock-controller@12010 {
+      compatible = "marvell,armada-3700-uart-clock";
+      reg = <0x12010 0x4>, <0x12210 0x4>;
+      clocks = <&tbg 0>, <&tbg 1>, <&tbg 2>, <&tbg 3>, <&xtalclk>;
+      clock-names = "TBG-A-P", "TBG-B-P", "TBG-A-S", "TBG-B-S", "xtal";
+      #clock-cells = <1>;
+    };