net: stmmac: convert plat->phylink_node to fwnode

All users of plat->phylink_node first convert it to a fwnode. Rather
than repeatedly convert to a fwnode, store it as a fwnode. To reflect
this change, call it plat->port_node instead - it is used for more
than just phylink.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/E1qZAX8-005pTo-OT@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>