ARM: dts: sun7i: Add Mele M3 board

The Mele M3 is yet another Allwinnner based Android top set box from Mele.

It uses a housing similar to the A2000, but without the USM sata storage slot
at the top.

It features an A20 SoC, 1G RAM, 4G eMMC (unique for Allwinner devices),
100Mbit ethernet, HDMI out, 3 USB A receptacles, VGA, and A/V OUT connections.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>