sun7i: Add defconfig for MSI Primo73 tablet

This patch uses the same DRAM settings as in the pre-installed
Android firmware. The LCD display is supported too.

Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>