dt-bindings: fsl: scu: add fallback compatible string for clock

SCU clock can be used in a similar way by IMX8QXP and IMX8QM SoCs.
Let's add a "fsl,scu-clk" fallback compatible string to allow other
SoCs to reuse the common part.

Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Sascha Hauer <kernel@pengutronix.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Michael Turquette <mturquette@baylibre.com>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

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

@@ -70,7 +70,9 @@ Clock bindings based on SCU Message Protocol
 This binding uses the common clock binding[1].
 
 Required properties:
-- compatible:		Should be "fsl,imx8qxp-clock".
+- compatible:		Should be one of:
+			  "fsl,imx8qxp-clock"
+			followed by "fsl,scu-clk"
 - #clock-cells:		Should be 1. Contains the Clock ID value.
 - clocks:		List of clock specifiers, must contain an entry for
 			each required entry in clock-names
@@ -137,7 +139,7 @@ firmware {
 			  &lsio_mu1 1 3>;
 
 		clk: clk {
-			compatible = "fsl,imx8qxp-clk";
+			compatible = "fsl,imx8qxp-clk", "fsl,scu-clk";
 			#clock-cells = <1>;
 		};