virtio: add virtio IDs file

Virtio IDs are spread all over the tree which makes assigning new IDs
bothersome. Putting them together should make the process less error-prone.

Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 3978923..200c22f 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -19,6 +19,7 @@
  */
 //#define DEBUG
 #include <linux/virtio.h>
+#include <linux/virtio_ids.h>
 #include <linux/virtio_balloon.h>
 #include <linux/swap.h>
 #include <linux/kthread.h>