km: ls102x: set ethrotate envvar to no

The default behavior in the latest u-boot revisions is to rotate the
active net device to the next available if the requested link is not
established.

For our ls102x based devices this would mean that if active debug net
device is not available, u-boot will rotate and set the next net device
that is one of the estar adapters.
To return from this situation manual action to set correct ethact
adapter will be needed and this can be annoying when working in
debug mode.

Setting ethrotate=no will disable net adapter rotation and will make sure
that the primary adapter is always used.

Signed-off-by: Aleksandar Gerasimovski <aleksandar.gerasimovski@hitachi-powergrids.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>