OpenBIOS build rules in QEMU's roms/Makefile

[BALATON Zoltan]

Hello,

I've noticed that the qemu/roms/Makefile that contains rules to build the 
firmwares that are included as a submodule and provided as binaries in the 
pc-bios dir is missing rules to build the OpenBIOS images in QEMU. Could 
you please submit a patch to add these rules to document how these 
binaries are correctly built and they are reproducible?

Thank you,
BALATON Zoltan