virtio-pci: add support for configure interrupt

Add support for configure interrupt, The process is used kvm_irqfd_assign
to set the gsi to kernel. When the configure notifier was signal by
host, qemu will inject a msix interrupt to guest

Signed-off-by: Cindy Lu <lulu@redhat.com>
Message-Id: <20211104164827.21911-11-lulu@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>