sun7i: Add new Bananapro board / defconfig

Add support for the new Bananapro A20 development board from lemaker.org.
This board features 1G RAM, 2 USB A receptacles, 1 micro USB receptacle for
OTG, 1 micro USB receptacle for power, HDMI, sata, Gbit ethernet, ir receiver,
3.5 mm jack for a/v out, on board microphone, 40 gpio pins and sdio wifi.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>