RGMII-ID uses an internal delay within the transmitter or receiver. This
feature is phy specific. The rest of the communication is normal RGMII.

So the fec driver has to check for all RGMII modes, not only
'PHY_INTERFACE_MODE_RGMII'.
Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>