virtio: Make vring_new_virtqueue support packed vring

It is used for testing in tools/virtio/vringh_test.c.
If vring_new_virtqueue supports packed vring, we can add support for
packed vring to vringh and test it.

Signed-off-by: Wenyu Huang <huangwenyu1998@gmail.com>
Message-Id: <20241013033233.65026-1-huangwenyu1998@gmail.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>