net: sparx5: add hostmode with phylink support

This patch adds netdevs and phylink support for the ports in the switch.
It also adds register based injection and extraction for these ports.

Frame DMA support for injection and extraction will be added in a later
series.

Signed-off-by: Steen Hegelund <steen.hegelund@microchip.com>
Signed-off-by: Bjarni Jonasson <bjarni.jonasson@microchip.com>
Signed-off-by: Lars Povlsen <lars.povlsen@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>