extending "buildrom"

[Stefan Reinauer]

Hi,

to get used to the config tool, I wrote the attached little patch
to change the buildrom command to allow specifying a filename of 
a rom file that is produced when building LinuxBIOS

i.e. 
  buildrom ROM_SIZE "normal" "fallback"
changed to:
  buildrom ./linuxbios.rom ROM_SIZE "normal" "fallback"

creating a linuxbios.rom file in the build target directory that
consists of the 2 concatenated romimages "normal" and "fallback"
This way it's now possible to build several roms with "buildrom"
that take the specified "romimage"s that were built. This could
i.e. be used to build several roms at once i.e.  with different 
payloads in them.

Is this ok to check in?