arm64: dts: allwinner: a64: Olinuxino: add Ethernet nodes

Add the DT nodes required to enable the Gigabit Ethernet on the board.
The PHY is powered by the always-on power rail VDD_SYS_3.3V (DCDC1).

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>