virtio: add vhost-user-fs-pci device

virtio: add vhost-user-fs-pci device

Add the PCI version of vhost-user-fs.

Launch QEMU like this:

  qemu -chardev socket,path=/tmp/vhost-fs.sock,id=chr0
       -device vhost-user-fs-pci,tag=myfs,chardev=chr0

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Message-Id: <20190930105135.27244-4-dgilbert@redhat.com>
Acked-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>