SR-IOV VFs are instantiated from their PF and intentionally do not
receive an ACPI handle by matching their runtime BDF.  Consequently,
ACPI locality queries for a VF fall back to the upstream bus.  This is
usually sufficient, but loses a _PXM supplied specifically for the PF.

Use the PCI core's owning-PF accessor for BUS_GET_DOMAIN and
BUS_GET_CPUS requests made for a VF.  This preserves the VF's lack of
an ACPI handle while allowing its CPU and NUMA placement to follow the
PF.

MFC after:      2 weeks