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: Haibo Chen <haibo.chen@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1629278277-7313-1-git-send-email-haibo.chen@nxp.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>