ARM: dts: BCM5301X: Add Ethernet interfaces links

Northstar SoCs have 3 usable Ethernet interfaces each connected to one
of switch ports. They all use fixed links.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Link: https://lore.kernel.org/r/20230707091519.21673-1-zajec5@gmail.com


Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>