[coreboot] Reliably build any Kconfig-based SeaBIOS revision

[Stefan Reinauer]

* Stefan Reinauer <stefan.reinauer at coreboot.org> [110203 22:33]:
> * Peter Stuge <peter at stuge.se> [110129 21:26]:
> > See patch.
> > 
> > The new TAG-stable points to the very latest commit in seabios.git,
> > which may not be quite right, but both stable and master must be
> > using Kconfig.
> > 
> > 
> > //Peter
> 
> slightly reworked to get rid of the perl calls (and to work with the
> latest HEAD version with options that are hidden during defconfig so a
> perl call would not replace them.
> 
> Reliably build arbitrary Kconfig-based revisions of SeaBIOS
>
> The reliability is accomplished by checking out the user's desired SeaBIOS
> tag into a branch named 'coreboot' in the local SeaBIOS git repository.
> Thanks to the use of a branch TAG-$(CONFIG_SEABIOS_..) can refer to any
> commitish at all in the SeaBIOS git repo.
>
> Configuration is done by make defconfig followed by enabling of several
> coreboot-specific Kconfig options for SeaBIOS using perl.
>
> Signed-off-by: Peter Stuge <peter at stuge.se>
> Acked-by: Stefan Reinauer <stefan.reinauer at coreboot.org>

Unless there's a reason not to, please commit the revised version (plus
the one line change to src/arch/x86/Makefile.inc which I forgot to diff)

Stefan