net: dsa: mv88e6xxx: accept phy-mode = "internal" for internal PHY ports

The ethernet-controller dt-schema, mostly pushed forward by Linux, has
the "internal" PHY mode for denoting MAC connections to an internal PHY.

U-Boot may provide device tree blobs where this phy-mode is specified,
so make the Linux driver accept them.

It appears that the current behavior with phy-mode = "internal" was
introduced when mv88e6xxx started reporting supported_interfaces to
phylink. Prior to that, I don't think it would have any issues accepting
this phy-mode.

Fixes: d4ebf12b ("net: dsa: mv88e6xxx: populate supported_interfaces and mac_capabilities")
Link: https://lore.kernel.org/linux-arm-kernel/20221205172709.kglithpbhdbsakvd@skbuf/T/Reported-by: NTim Harvey <tharvey@gateworks.com>
Signed-off-by: NVladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: NFlorian Fainelli <f.fainelli@gmail.com>
Tested-by: Tim Harvey <tharvey@gateworks.com> # imx6q-gw904.dts
Link: https://lore.kernel.org/r/20221205194845.2131161-1-vladimir.oltean@nxp.comSigned-off-by: NPaolo Abeni <pabeni@redhat.com>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -833,10 +833,13 @@ static void mv88e6xxx_get_caps(struct dsa_switch *ds, int port,
 
 	chip->info->ops->phylink_get_caps(chip, port, config);
 
-	/* Internal ports need GMII for PHYLIB */
-	if (mv88e6xxx_phy_is_internal(ds, port))
+	if (mv88e6xxx_phy_is_internal(ds, port)) {
+		__set_bit(PHY_INTERFACE_MODE_INTERNAL,
+			  config->supported_interfaces);
+		/* Internal ports with no phy-mode need GMII for PHYLIB */
 		__set_bit(PHY_INTERFACE_MODE_GMII,
 			  config->supported_interfaces);
+	}
 }
 
 static void mv88e6xxx_mac_config(struct dsa_switch *ds, int port,