arm64: dts: ls1028a: set up the real link speed for ENETC port 2

arm64: dts: ls1028a: set up the real link speed for ENETC port 2

In NXP LS1028A there is a MAC-to-MAC internal link between enetc_port2
and mscc_felix_port4. This link operates at 2.5Gbps and is described as
such for the mscc_felix_port4 node.

The reason for the discrepancy is a limitation in the PHY library
support for fixed-link nodes. Due to the fact that the PHY library
registers a software PHY which emulates the clause 22 register map, the
drivers/net/phy/fixed_phy.c driver only supports speeds up to 1Gbps.

The mscc_felix_port4 node is probed by DSA, which does not use the PHY
library directly, but phylink, and phylink has a different representation
for fixed-link nodes, one that does not have the limitation of not being
able to represent speeds > 1Gbps.

Since the enetc driver was converted to phylink too as of commit
71b77a7a27a3 ("enetc: Migrate to PHYLINK and PCS_LYNX"), the limitation
has been practically lifted there too, and we can describe the real link
speed in the device tree now.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>