vsock/virtio: factor our the code to initialize and delete VQs

Add virtio_vsock_vqs_init() and virtio_vsock_vqs_del() with the code
that was in virtio_vsock_probe() and virtio_vsock_remove to initialize
and delete VQs.

These new functions will be used in the next commit to support device
suspend/resume

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>