Thank your very much! I was able to extract the ROM using the mapped memory method listed at the end of that article. I am sort of bummed out by the generated ROM file however, because it does not seem to support EFI according to this article: http://vfio.blogspot.com/2014/08/does-my-graphics-card-rom-support-efi.html. Does this sound right?
you might be able to achieve what you want by following one of the
procedures described in the coreboot wiki, especially http://coreboot.org/VGA_support#UEFI_Method
Good luck!
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Kind regards/Mit freundlichen Grüßen, Stefan Tauner