Comment # 1 on bug 1126990 from Liang Yan

Did some investigation, it looks there is no PM implementation in driver at
all.

https://elixir.bootlin.com/linux/v5.0-rc8/source/net/9p/trans_virtio.c


static unsigned int features[] = {
    VIRTIO_9P_MOUNT_TAG,
};

/* The standard "struct lguest_driver": */
static struct virtio_driver p9_virtio_drv = {
    .feature_table  = features,
    .feature_table_size = ARRAY_SIZE(features),
    .driver.name    = KBUILD_MODNAME,
    .driver.owner    = THIS_MODULE,
    .id_table    = id_table,
    .probe        = p9_virtio_probe,
    .remove        = p9_virtio_remove,
};