I don't know if this is a bug but when i use the name "pci100b,0030.rom" for the vgabios it is still not loading it. It would be nice to be able to add the vgabios to cbfs via the existing coreboot kconfig option.
Something's not right with the way the PCI device is configured. You could try putting debug statements in is_pci_vga() to find out what.
I fixed this problem. The PCI_COMMAND_IO bit was not set in the VGA PCI space.