net: enetc: add preliminary support for i.MX95 ENETC PF

The i.MX95 ENETC has been upgraded to revision 4.1, which is different
from the LS1028A ENETC (revision 1.0) except for the SI part. Therefore,
the fsl-enetc driver is incompatible with i.MX95 ENETC PF. So add new
nxp-enetc4 driver to support i.MX95 ENETC PF, and this driver will be
used to support the ENETC PF with major revision 4 for other SoCs in the
future.

Currently, the nxp-enetc4 driver only supports basic transmission feature
for i.MX95 ENETC PF, the more basic and advanced features will be added
in the subsequent patches. In addition, PCS support has not been added
yet, so 10G ENETC (ENETC instance 2) is not supported now.

Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>