seabios: add ati vgabios binary

Built from master (commit 6e56ed129c9782ba050a5fbfbf4ac12335b230f7),
which has ati vgabios support merged (checkout master branch in
roms/seabios submodule, then run "make -C roms seavgabios-ati").

Temporary exception until the next seabios major version is
released (probably 1.13, fall 2019).

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Tested-by: BALATON Zoltan <balaton@eik.bme.hu>
Message-id: 20190620151104.2678-3-kraxel@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>