ARM: dts: sun8i: a83t: Enable Ethernet on two boards

The Cubietruck Plus has a Realtek RTL8211E RGMII PHY tied to the EMAC.
The AXP818 PMIC's regulators provide main power and secondary signaling
voltages to the PHY. The latter is always on, as it also supplies the
pingroup on the SoC, which has other uses.

The Bananapi M3 has a Realtek RTL8211E RGMII PHY tied to the EMAC.
The AXP818 PMIC's SW regulators provides power to the PHY.

This patch enables Ethernet with the EMAC on both these boards by
enabling the emac node and setting all the required properties.
A proper ethernet alias is added as well.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>