Rather than erroring out, I think it may be better to just adopt
the Marvell solution to this problem to give consistent behaviour
across all PHYs.

Yes, expand phy_config_aneg() to look for this condition and enable
autoneg. But should we disable it when the condition is reverted? The
user swaps to 100Mbps forced?

What about other speeds? Is this limited to 1G? Since we have devices
without auto-neg for 2500BaseX i assume it is not an issue there.

	Andrew