A20: add H6S hd12-a20 sugar-jes_8188eus

This patch adds the fex file for the hd12-a20, on the wiki known as H6S.
The board marks it as hd12-a20 and the fex file calls itself the
sugar-jes_8188eus.

Not sure about the io/bus widths here, they are listed as 16, which is
possible as there's 2 ram sockets left empty totaling 512 MiB.