net: dsa: felix: accept "ethernet-ports" OF node name

Since both forms are accepted, let's search for both when we
pre-validate the PHY modes.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>