adds board enable for ABIT AV8.
I compared the download pages of both, abit AV8 and abit AV8-3rd Eye, and the BIOS downloads are the same. So it's save to assume that this board enable works on both revisions of abit AV8. (Tested on AV8)
Signed-off-by: Christoph Grenz <christophg+cb at grenz-bonn.de>