Some SiS boards won't boot without pci=bios forcing their method.
The reason for this is in the probe method, we try the BIOS method, and it
succeeds and we store the pci_ops. We then try the direct access, it fails
and we trash the old pci_ops.
The patch stores the pci_ops when BIOS method succeeds and restores it
if the direct hardware access method fails.