arm64: allwinner: h5: add support for the Orange Pi PC 2 board

The Orange Pi PC 2 is a typical single board computer using the
Allwinner H5 SoC. Apart from the usual suspects it features three
separately driven USB ports and a Gigabit Ethernet port.
Also it has a SPI NOR flash soldered, from which the board can boot
from. This enables the SBC to behave like a "real computer" with
built-in firmware.

Add the board specific .dts file, which includes the H5 .dtsi and
enables the peripherals that we support so far.

Reviewed-by: Rask Ingemann Lambertsen <rask@formelder.dk>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
[Icenowy: dropped all GPIO pinctrl nodes, change red LED gpio,
 change MMC cd to active-low, rename some node names to prevent
 underscores]
Signed-off-by: Icenowy Zheng <icenowy@aosc.xyz>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>