Enable both the MACs found on the board.

ethernet0 and ethernet1 both ultimately go to a series of on board
switches which aren't managed by this processor.

ethernet0 is connected to a Marvell 88EA1512 phy via RGMII. That goes to
the series of switches via SGMII on the "media" side of the phy.
RGMII_SGMII mode is enabled via devicetree register descriptions.
The switch on the "media" side has auto-negotiation disabled, so
configuration from userspace similar to:

        ethtool -s eth0 autoneg off speed 1000 duplex full

is necessary to get traffic flowing on that interface.

ethernet1 is in a mac2mac/fixed-link configuration going to the same
series of switches directly via RGMII.
Tested-by: Brian Masney <bmasney@redhat.com>
Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
Reviewed-by: Brian Masney <bmasney@redhat.com>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230501205105.2518373-3-ahalaney@redhat.com