net: dsa: b53: add support for BCM63xx RGMIIs

BCM63xx RGMII ports require additional configuration in order to work.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20230319220805.124024-1-noltari@gmail.com


Signed-off-by: Paolo Abeni <pabeni@redhat.com>