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-snap.c b/drivers/md/dm-snap.c
index e1dcca9..1ba8a47 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -18,10 +18,10 @@
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 #include <linux/log2.h>
+#include <linux/dm-kcopyd.h>
 
 #include "dm-snap.h"
 #include "dm-bio-list.h"
-#include "kcopyd.h"
 
 #define DM_MSG_PREFIX "snapshots"