pci_user: Report NUMA domain

A PCI device's NUMA domain is now accessible via the pd_numa_domain
member of struct pci_conf when using the PCIOCGETCONF ioctl.

A new ioctl number has been assigned to PCIOCGETCONF to preserve
compatibility with binaries compiled on FreeBSD versions 7 through 14.
Such binaries can continue to use the PCIOCGETCONF ioctl number
that they were compiled with and experience no ABI repercussions.

Reviewed by: imp, markj
Differential Revision: https://reviews.freebsd.org/D44289