net: dsa: lantiq_gswip: Only allow phy-mode = "internal" on the CPU port

net: dsa: lantiq_gswip: Only allow phy-mode = "internal" on the CPU port

Add the CPU port to gswip_xrx200_phylink_get_caps() and
gswip_xrx300_phylink_get_caps(). It connects through a SoC-internal bus,
so the only allowed phy-mode is PHY_INTERFACE_MODE_INTERNAL.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Acked-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: Martin Schiller <ms@dev.tdt.de>
Link: https://lore.kernel.org/r/20240611135434.3180973-3-ms@dev.tdt.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>