dt-bindings: Add binding for i.MX8MQ CCM

This adds the binding for the i.MX8MQ Clock Controller Module.
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

Documentation/devicetree/bindings/clock/imx8mq-clock.txt

+* Clock bindings for NXP i.MX8M Quad
+
+Required properties:
+- compatible: Should be "fsl,imx8mq-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:
+    - "ckil"
+    - "osc_25m"
+    - "osc_27m"
+    - "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/imx8mq-clock.h
+for the full list of i.MX8M Quad clock IDs.