arch: arm: dts: fsl-lx2160a.dtsi: sync serial nodes with Linux

Sync the serial nodes of the LX2160A based boards with their
representation in Linux. We also imported the clockgen and sysclk nodes
which are dependencies.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>