Drop some headers from mm.h

mm.h doesn't use directly anything from mutex.h and backing-dev.h, so
remove them and add them back to files which need them.

Cross-compile tested on many configs and archs.
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/afs/write.c

@@ -8,7 +8,7 @@
  * as published by the Free Software Foundation; either version
  * 2 of the License, or (at your option) any later version.
  */
-
+#include <linux/backing-dev.h>
 #include <linux/slab.h>
 #include <linux/fs.h>
 #include <linux/pagemap.h>

include/linux/mm.h

@@ -10,9 +10,7 @@
 #include <linux/mmzone.h>
 #include <linux/rbtree.h>
 #include <linux/prio_tree.h>
-#include <linux/mutex.h>
 #include <linux/debug_locks.h>
-#include <linux/backing-dev.h>
 #include <linux/mm_types.h>
 
 struct mempolicy;

mm/fremap.c

@@ -5,7 +5,7 @@
  *
  * started by Ingo Molnar, Copyright (C) 2002, 2003
  */
-
+#include <linux/backing-dev.h>
 #include <linux/mm.h>
 #include <linux/swap.h>
 #include <linux/file.h>

mm/mmap.c

@@ -7,6 +7,7 @@
  */
 
 #include <linux/slab.h>
+#include <linux/backing-dev.h>
 #include <linux/mm.h>
 #include <linux/shm.h>
 #include <linux/mman.h>

mm/truncate.c

@@ -8,6 +8,7 @@
  */
 
 #include <linux/kernel.h>
+#include <linux/backing-dev.h>
 #include <linux/mm.h>
 #include <linux/swap.h>
 #include <linux/module.h>