qemu: Introduce qemuDomainNetIsPCI()

qemu: Introduce qemuDomainNetIsPCI()

This centralizes the knowledge about which network interface
models are PCI devices and thus need to have a PCI address
allocated by libvirt, and expands said knowledge to include
the fact that models such as spapr-vlan and smc91c111 are
not PCI devices.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>