dt-bindings: mmc: fsl-imx-esdhc: add a new compatible string

Lack a compatible string "fsl,imx6sll-usdhc", so add it here.
Signed-off-by: NHaibo Chen <haibo.chen@nxp.com>
Acked-by: NRob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1629278277-7313-1-git-send-email-haibo.chen@nxp.comSigned-off-by: NUlf Hansson <ulf.hansson@linaro.org>

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

@@ -29,6 +29,7 @@ properties:
           - fsl,imx53-esdhc
           - fsl,imx6q-usdhc
           - fsl,imx6sl-usdhc
+          - fsl,imx6sll-usdhc
           - fsl,imx6sx-usdhc
           - fsl,imx6ull-usdhc
           - fsl,imx7d-usdhc