PCI: Move pci_read_vpd() and pci_write_vpd() close to other VPD code

pci_read_vpd() and pci_write_vpd() were stranded in the middle of config
accessor functions.  Move them close to the other VPD code in the file.
No functional change.

Tested-by: Shane Seymour <shane.seymour@hpe.com>
Tested-by: Babu Moger <babu.moger@oracle.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>