[POWERPC] net: NEWEMAC: Remove "rgmii-interface" from rgmii matching table

With the removal the the "rgmii-interface" device_type property from the
dts files, the newemac driver needs an update to only rely on compatible
property.

Signed-off-by: Stefan Roese <sr@denx.de>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>