Per default, use SeaBIOS payload instead of no payload.

Per default, use SeaBIOS payload instead of no payload.
Add choice to use stable or master version of seabios repository

Signed-off-by: Stefan Reinauer <stepan@coreboot.org>
Acked-by: Stefan Reinauer <stepan@coreboot.org>
git-svn-id: svn://svn.coreboot.org/coreboot/trunk@6223 2b7e53f0-3cfb-0310-b3e9-8179ed1497e1