arm64: dts: layerscape: remove big-endian for mmc nodes

According to binding doc fsl,esdhc.yaml, the default endian mode is
big-endian. So remove big-endian property to fix below CHECK_DTBS warnings:

arm64/boot/dts/freescale/fsl-ls1012a-qds.dtb: mmc@1560000: Unevaluated properties are not allowed ('big-endian' was unexpected)
        from schema $id: http://devicetree.org/schemas/mmc/fsl,esdhc.yaml



Signed-off-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>