dt-bindings: clk: imx: Add fsl,scu-clk yaml file

In order to replace the fsl,scu txt file from bindings/arm/freescale,
we need to split it between the right subsystems. This patch documents
separately the 'clock' child node of the SCU main node.

Signed-off-by: Abel Vesa <[e-mail]>
Signed-off-by: Viorel Suman <[e-mail]>
Acked-by: Stephen Boyd <[e-mail]>
Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Shawn Guo <[e-mail]>

Documentation/devicetree/bindings/arm/freescale/fsl,scu.txt

···
 			See detailed Resource ID list from:
 			include/dt-bindings/firmware/imx/rsrc.h
 
-Clock bindings based on SCU Message Protocol
-------------------------------------------------------------
-
-This binding uses the common clock binding[1].
-
-Required properties:
-- compatible:		Should be one of:
-			  "fsl,imx8dxl-clk"
-			  "fsl,imx8qm-clk"
-			  "fsl,imx8qxp-clk"
-			followed by "fsl,scu-clk"
-- #clock-cells:		Should be 2.
-			Contains the Resource and Clock ID value.
-- clocks:		List of clock specifiers, must contain an entry for
-			each required entry in clock-names
-- clock-names:		Should include entries "xtal_32KHz", "xtal_24MHz"
-
-The clock consumer should specify the desired clock by having the clock
-ID in its "clocks" phandle cell.
-
-See the full list of clock IDs from:
-include/dt-bindings/clock/imx8qxp-clock.h
-
 Pinctrl bindings based on SCU Message Protocol
 ------------------------------------------------------------
 
···
 			Please refer to i.MX8QXP Reference Manual for detailed
 			CONFIG settings.
 
-[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
 [2] Documentation/devicetree/bindings/power/power-domain.yaml
 [3] Documentation/devicetree/bindings/pinctrl/fsl,imx-pinctrl.txt
 
···
 			  &lsio_mu1 1 3
 			  &lsio_mu1 3 3>;
 
-		clk: clk {
-			compatible = "fsl,imx8qxp-clk", "fsl,scu-clk";
-			#clock-cells = <2>;
-		};
-
 		iomuxc {
 			compatible = "fsl,imx8qxp-iomuxc";
 
···
 	...
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_lpuart0>;
-	clocks = <&uart0_clk IMX_SC_R_UART_0 IMX_SC_PM_CLK_PER>;
-	clock-names = "ipg";
 	power-domains = <&pd IMX_SC_R_UART_0>;
 };

Documentation/devicetree/bindings/clock/fsl,scu-clk.yaml

···
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/clock/fsl,scu-clk.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: i.MX SCU Client Device Node - Clock bindings based on SCU Message Protocol
+
+maintainers:
+  - Abel Vesa <[e-mail]>
+
+description: i.MX SCU Client Device Node
+  Client nodes are maintained as children of the relevant IMX-SCU device node.
+  This binding uses the common clock binding.
+  (Documentation/devicetree/bindings/clock/clock-bindings.txt)
+  The clock consumer should specify the desired clock by having the clock
+  ID in its "clocks" phandle cell. See the full list of clock IDs from
+  include/dt-bindings/clock/imx8qxp-clock.h
+
+properties:
+  compatible:
+    items:
+      - enum:
+          - fsl,imx8dxl-clk
+          - fsl,imx8qm-clk
+          - fsl,imx8qxp-clk
+      - const: fsl,scu-clk
+
+  '#clock-cells':
+    const: 2
+
+required:
+  - compatible
+  - '#clock-cells'
+
+additionalProperties: false
+
+examples:
+  - |
+    clock-controller {
+        compatible = "fsl,imx8qxp-clk", "fsl,scu-clk";
+        #clock-cells = <2>;
+    };