sunxi: Add OrangePi PC 2 initial support

The OrangePi PC 2 is a typical SBC with the 64-bit Allwinner H5 SoC.
Add a (64-bit only) defconfig defining the required options to build
the U-Boot proper.

Create a new .dts file for it by including the (32-bit) H3 SoC .dtsi
and changing the differing components accordingly.
This is a preliminary device tree mostly for U-Boot's own sake, it
is expected to be updated once the official DT gets accepted upstream.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
[squash the commits, update the commit message]
Signed-off-by: Jagan Teki <jagan@openedev.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>