Add the required DT parts to enable Ethernet (dwmac-sun8i driver) on
the Orange Pi Prime board. It uses an external Realtek RTL8211E PHY
connected via RGMII to provide GbE network.

This includes the regulator (which is controlled by a GPIO pin) and
the actual Ethernet MAC node, referring the RGMII pins of the device.
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>