seabios: do normal config, disable oprom in vgarom

previously, "normal" initmode relied on the vgarom-based
seabios config, which enables option roms, but then lbmk
would insert pci-optionrom-exec 0 for vgarom, and 2 for normal

in libreboot, coreboot roms with "vgarom" in the filename do
pci option rom execution from coreboot, and "normal" roms
do execution from seabios(where seabios is the only payload
provided on normal setups)

this is because payloads like grub can also be used, on vgarom
setups, where coreboot must handle oprom execution