arm64: allwinner: h6: add support for the Ethernet on Pine H64

The Pine H64 board has an Ethernet port, which is connected to a
RTL8211E PHY, then the PHY is connected to the MAC on H6 SoC.

Add support for the Ethernet port.

The PHY needs some time to start up, and the time is modelled as enable
ramp delay of the regulator.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>