ARM: dts: ls1021a: remove undocumented 'big-endian' for memory-controller node

ARM: dts: ls1021a: remove undocumented 'big-endian' for memory-controller node

According to binding doc mmc/fsl,esdhc.yaml and driver
drivers/mmc/host/sdhci-of-esdhc.c, default is big-endian, should
use little-endian for little-endian system. Remove 'big-endian' to fix
below warning:

esdhc@1560000 (fsl,ls1021a-esdhc): Unevaluated properties are not allowed ('big-endian', 'bus-width' were unexpected)

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>