pci: allow override of PCI vendor/device ids

pci: allow override of PCI vendor/device ids

This allows mobile- and vGPUs to be presented to the guest as if they
were the original desktop variants of the card. It also allows
device-ID variants that guests don't know about to be renamed to
match compatible sibling devices the guest does have drivers for
(e.g. to remove manufacturer-specific vendor ID variants that prevent
the use of a device which would otherwise have a supported chipset)

e.g. hostpci0: 03:00,vendor-id=0x8086,device-id=0x10f6

Signed-off-by: Nicholas Sherlock <n.sherlock@gmail.com>
Reviewed-by: Dominik Csapak <d.csapak@proxmox.com>
Tested-by: Dominik Csapak <d.csapak@proxmox.com>