dt-bindings: imx: Add clock binding doc for i.MX8MP

Add the clock binding doc for i.MX8MP.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Abel Vesa <abel.vesa@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

Documentation/devicetree/bindings/clock/imx8mp-clock.yaml

+# SPDX-License-Identifier: GPL-2.0
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/bindings/clock/imx8mp-clock.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: NXP i.MX8M Plus Clock Control Module Binding
+
+maintainers:
+  - Anson Huang <Anson.Huang@nxp.com>
+
+description:
+  NXP i.MX8M Plus clock control module is an integrated clock controller, which
+  generates and supplies to all modules.
+
+properties:
+  compatible:
+    const: fsl,imx8mp-ccm
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    items:
+      - description: 32k osc
+      - description: 24m osc
+      - description: ext1 clock input
+      - description: ext2 clock input
+      - description: ext3 clock input
+      - description: ext4 clock input
+
+  clock-names:
+    items:
+      - const: osc_32k
+      - const: osc_24m
+      - const: clk_ext1
+      - const: clk_ext2
+      - const: clk_ext3
+      - const: clk_ext4
+
+  '#clock-cells':
+    const: 1
+    description:
+      The clock consumer should specify the desired clock by having the clock
+      ID in its "clocks" phandle cell. See include/dt-bindings/clock/imx8mp-clock.h
+      for the full list of i.MX8M Plus clock IDs.
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - clock-names
+  - '#clock-cells'
+
+examples:
+  # Clock Control Module node:
+  - |
+    clk: clock-controller@30380000 {
+        compatible = "fsl,imx8mp-ccm";
+        reg = <0x30380000 0x10000>;
+        #clock-cells = <1>;
+        clocks = <&osc_32k>, <&osc_24m>, <&clk_ext1>,
+                 <&clk_ext2>, <&clk_ext3>, <&clk_ext4>;
+        clock-names = "osc_32k", "osc_24m", "clk_ext1",
+                      "clk_ext2", "clk_ext3", "clk_ext4";
+    };
+
+...