kvm: i386: Add classic PCI device assignment

kvm: i386: Add classic PCI device assignment

This adds PCI device assignment for i386 targets using the classic KVM
interfaces. This version is 100% identical to what is being maintained
in qemu-kvm for several years and is supported by libvirt as well. It is
expected to remain relevant for another couple of years until kernels
without full-features and performance-wise equivalent VFIO support are
obsolete.

A refactoring to-do that should be done in-tree is to model MSI and
MSI-X support via the generic PCI layer, similar to what VFIO is already
doing for MSI-X. This should improve the correctness and clean up the
code from duplicate logic.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Acked-by: Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>