sunxi:boards: add a13 pov mobii 703 tablet

Aka Q8.

Signed-off-by: Luc Verhaegen <libv@skynet.be>
sunxi:boards: add forfun q88db tablet

Signed-off-by: Luc Verhaegen <libv@skynet.be>
sunxi:boards: add Merrii Hummingbird A20

This uses the same dram settings as cubieboard2 and iteaduino A20

Signed-off-by: Luc Verhaegen <libv@skynet.be>