sunxi: defconfig: Add X96 Mate TV box

sunxi: defconfig: Add X96 Mate TV box

The X96 Mate TV box is a TV box with the Allwinner H616 SoC. It is
available with up to 4GB of DRAM and 64GB eMMC.
The DRAM chips require a different configuration when compared to the
OrangePi Zero2, we must not use read/write training and write leveling.

Add a defconfig for the box, so that we can easily build U-Boot for it.
We synced the .dts file already from the kernel tree.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>