sun5i: Add defconfig and dts file for the Empire Electronix M712 tablet

Add a defconfig and dts file for the Empire Electronix M712 tablet, this
is a 7" A13 tablet, with micro-usb (otg), headphone and micro-sd slots on
the outside. It uses a Goodix gt811 touchscreen controller, a RTL8188CTV
wifi chip and a DMART06 (1238a4) accelerometer.

The dts file is identical to the one submitted to the upstream kernel.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>