virtio: let header files include virtio_ids.h

Rusty,

commit 3ca4f5ca73057a617f9444a91022d7127041970a
    virtio: add virtio IDs file
moved all device IDs into a single file. While the change itself is
a very good one, it can break userspace applications. For example
if a userspace tool wanted to get the ID of virtio_net it used to
include virtio_net.h. This does no longer work, since virtio_net.h
does not include virtio_ids.h.
This patch moves all "#include <linux/virtio_ids.h>" from the C
files into the header files, making the header files compatible with
the old ones.

In addition, this patch exports virtio_ids.h to userspace.

CC: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/include/linux/virtio_console.h b/include/linux/virtio_console.h
index b5f5198..fe88517 100644
--- a/include/linux/virtio_console.h
+++ b/include/linux/virtio_console.h
@@ -1,6 +1,7 @@
 #ifndef _LINUX_VIRTIO_CONSOLE_H
 #define _LINUX_VIRTIO_CONSOLE_H
 #include <linux/types.h>
+#include <linux/virtio_ids.h>
 #include <linux/virtio_config.h>
 /* This header, excluding the #ifdef __KERNEL__ part, is BSD licensed so
  * anyone can use the definitions to implement compatible drivers/servers. */