migration: Create migration/blocker.h

This allows us to remove lots of includes of migration/migration.h

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
diff --git a/stubs/migr-blocker.c b/stubs/migr-blocker.c
index a5ba18f..2b64ac9 100644
--- a/stubs/migr-blocker.c
+++ b/stubs/migr-blocker.c
@@ -1,6 +1,6 @@
 #include "qemu/osdep.h"
 #include "qemu-common.h"
-#include "migration/migration.h"
+#include "migration/blocker.h"
 
 int migrate_add_blocker(Error *reason, Error **errp)
 {