board: sl28: add network variant 1 support

This variant has one network port connected via RGMII and doesn't have
any TSN capabilities out-of-the-box. Instead it has all four SerDes
lanes available for customer use.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>
5 files changed