sunxi: DT: A64: add proper SoPine baseboard device tree

When the defconfig for the SoPine baseboard was added, there wasn't any
proper DT for the board yet, so we used the Pine64 DT as a placeholder.
Copy the DT file(s) meanwhile added in Linux over to U-Boot, and use
them in our defconfig.
This is as of v4.18-rc3, exactly Linux commit:
commit 7d556bfc49adddf2beb0d16c91945c3b8b783282
Author: Jagan Teki <jagannadh.teki@gmail.com>
Date:   Mon Dec 4 10:23:07 2017 +0530

    arm64: allwinner: a64-sopine: Fix to use dcdc1 regulator instead of vcc3v3

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Acked-by: Jagan Teki <jagan@amarulasolutions.com>