Add PCIV_INVALID definition

From PCI Spec rev 2.2, 6.2.1. Device Identification:
Vendor ID This field identifies the manufacturer of the device. Valid
vendor identifiers are allocated by the PCI SIG to ensure uniqueness.
0FFFFh is an invalid value for Vendor ID.

MFC after: 3 days
Approved by: re (Glen), hselasky (mentor), kib (mentor)
Sponsored by: Mellanox Technologies