ARM: dts: sun9i: cubieboard4: Enable GMAC

The Cubieboard4 has a Realtek RTL8211E ethernet PHY which uses RGMII to
talk to the MAC. The PHY is powered by 2 regulators: cldo1 for the PHY's
core logic and gpio1-ldo for I/O. The latter also powers the SoC side
pins. As there is no binding to model a second regulator supply for the
PHY, it is omitted. It is however properly modeled for the PIO.

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