Simplified pci_fill_info() and friends

Simplified pci_fill_info() and friends

Previously, we kept track of which fields were already filled, which
was quite brittle.

Now we keep only the set of already known fields in struct pci_dev.
We check if the current field is needed against this information.

Not only this simplifies the whole thing, but it also enables future
back-ends to call pci_fill_info() recursively as needed.