net: sun8i-emac: remove support for old binding

The original DT binding used by U-Boot's sun8i-emac driver was not really
agreed upon, and deviated from the "official" binding now used by the
kernel. Since now all U-Boot users have been converted to the new
binding, we can remove support for the old DT nodes from the driver.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>