dt-bindings: imx: Add clock binding doc for imx8mm

Add the clock binding doc for i.MX8MM.

Signed-off-by: Bai Ping <ping.bai@nxp.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

Documentation/devicetree/bindings/clock/imx8mm-clock.txt

@@ -0,0 +1,29 @@
+* Clock bindings for NXP i.MX8M Mini
+
+Required properties:
+- compatible: Should be "fsl,imx8mm-ccm"
+- reg: Address and length of the register set
+- #clock-cells: Should be <1>
+- clocks: list of clock specifiers, must contain an entry for each required
+          entry in clock-names
+- clock-names: should include the following entries:
+    - "osc_32k"
+    - "osc_24m"
+    - "clk_ext1"
+    - "clk_ext2"
+    - "clk_ext3"
+    - "clk_ext4"
+
+clk: clock-controller@30380000 {
+	compatible = "fsl,imx8mm-ccm";
+	reg = <0x0 0x30380000 0x0 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";
+};
+
+The clock consumer should specify the desired clock by having the clock
+ID in its "clocks" phandle cell. See include/dt-bindings/clock/imx8mm-clock.h
+for the full list of i.MX8M Mini clock IDs.