dt-bindings: mmc: fsl-imx-esdhc: add imx8m compatible string

Add imx8mq/m/n compatible string
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/fsl-imx-esdhc.txt

@@ -18,6 +18,9 @@ Required properties:
 	       "fsl,imx6ull-usdhc"
 	       "fsl,imx7d-usdhc"
 	       "fsl,imx7ulp-usdhc"
+	       "fsl,imx8mq-usdhc"
+	       "fsl,imx8mm-usdhc"
+	       "fsl,imx8mn-usdhc"
 	       "fsl,imx8qxp-usdhc"
 
 Optional properties: