arm: dts: lx2160ardb: support eMMC HS400 mode

Add properties related to eMMC HS400 mode.

mmc-hs400-1_8v;
bus-width = <8>;

They had been already in kernel dts file since the first
lx2160ardb dts patch.

b068890 arm64: dts: add LX2160ARDB board support

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>