net: dsa: felix: Use PHY_INTERFACE_MODE_INTERNAL instead of GMII

net: dsa: felix: Use PHY_INTERFACE_MODE_INTERNAL instead of GMII

phy-mode = "gmii" is confusing because it may mean that the port
supports the 8-bit-wide parallel data interface pinout, which it
doesn't.

It may also be confusing because one of the "gmii" internal ports is
actually overclocked to run at 2.5Gbps (even though, yes, as far as the
switch MAC is concerned, it still thinks it's gigabit).

So use the phy-mode = "internal" property to describe the internal ports
inside the NXP LS1028A chip (the ones facing the ENETC). The change
should be fine, because the device tree bindings document is yet to be
introduced, and there are no stable DT blobs in use.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Michael Walle <michael@walle.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>