dm: move include files

Publish the dm-io, dm-log and dm-kcopyd headers in include/linux.

Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
index 978c041..ed9c86c 100644
--- a/drivers/md/dm-io.c
+++ b/drivers/md/dm-io.c
@@ -5,7 +5,6 @@
  * This file is released under the GPL.
  */
 
-#include "dm-io.h"
 #include "dm.h"
 
 #include <linux/bio.h>
@@ -13,6 +12,7 @@
 #include <linux/module.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
+#include <linux/dm-io.h>
 
 struct dm_io_client {
 	mempool_t *pool;