sunxi: Add softwinner astar mid756 A33 tablet board defconfig

The Astar MID756 is a 7" tablet using the A33 SoC with a 800x480 LCD screen,
512M RAM, 8G ROM and integrated sdio wifi.

Also see: http://linux-sunxi.org/Softwinner_astar-rda



Signed-off-by: Vishnu Patekar <vishnupatekar0510@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>