PCI: Expand "VPD access disabled" quirk message

It's not very enlightening to see

  pci 0000:07:00.0: [Firmware Bug]: VPD access disabled

in the dmesg log because there's no clue about what the firmware bug is.
Expand the message to explain why we're disabling VPD.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>