board/km: add support for expu1 design based on nxp

The EXPU1 design is a new 40G capable ethernet service unit card for
Hitachi-Powergrids wired-com product lines.

The base SoC is same as for already added SELI8 card, consequently the
already added u-boot support for SELI8 is reused.

Signed-off-by: Rainer Boschung <rainer.boschung@hitachi-powergrids.com>
Signed-off-by: Aleksandar Gerasimovski <aleksandar.gerasimovski@hitachi-powergrids.com>
[Fixed new line error at EOF]
Signed-off-by: Priyanka Jain <priyanka.jain@nxp.com>