[coreboot] Absolute paths in configs and redundant pci_rom ids

[Myles Watson]

> > +#pci_rom ../../../misc/kontron-pci8086,27a2.rom vendor_id=0x8086
> device_id=0x27a2
> 
> Can we improve these relative paths somehow?
> 
> Maybe use a variable as top instead? $(TOP)/misc/ ... ?
> 
> Absolute or relative does not matter, but so many parent directories
> is horrible to have to keep track of.
> 
> 
> And vendor_id/device_id looks like they will become highly redundant.
> I'd like to either leave out the filename or the ids. Comments?

This is just an example line.  Notice that it is commented out.  It could
just have easily been:

pci_rom ../kontron-vga.rom vendor_id=0x8086 device_id=0x27a2
or
pci_rom /tmp/Kontron-vga.rom vendor_id=0x8086 device_id=0x27a2

Since we find option ROMs based on the PCI IDs I think it makes sense to
have them specified explicitly here.  Otherwise we need to trust the user to
form the filename correctly.

Thanks,
Myles