actually specify valid bases that should be treated just as normal.
The PCI specifications have no indication that 0 would be a magic value
indicating a disabled BAR as commonly used on at least amd64 and i386
but not sparc64. It's unclear what to do in pci_delete_resource()
instead of writing 0 to a BAR though as there's no (other) way do
disable individual BARs so its decoding is left enabled in case of
__PCI_BAR_ZERO_VALID for now.
Approved by: re (kib), jhb
MFC after: 1 week
109d6f3c87