headers: untangle kmemleak.h from mm.h

Currently <linux/slab.h> #includes <linux/kmemleak.h> for no obvious
reason.  It looks like it's only a convenience, so remove kmemleak.h
from slab.h and add <linux/kmemleak.h> to any users of kmemleak_* that
don't already #include it.  Also remove <linux/kmemleak.h> from source
files that do not use it.

This is tested on i386 allmodconfig and x86_64 allmodconfig.  It would
be good to run it through the 0day bot for other $ARCHes.  I have
neither the horsepower nor the storage space for the other $ARCHes.

Update: This patch has been extensively build-tested by both the 0day
bot & kisskb/ozlabs build farms.  Both of them reported 2 build failures
for which patches are included here (in v2).

[ slab.h is the second most used header file after module.h; kernel.h is
  right there with slab.h. There could be some minor error in the
  counting due to some #includes having comments after them and I didn't
  combine all of those. ]

[[email protected]: security/keys/big_key.c needs vmalloc.h, per sfr]
Link: http://lkml.kernel.org/r/[email protected]
Link: http://kisskb.ellerman.id.au/kisskb/head/13396/
Signed-off-by: Randy Dunlap <[email protected]>
Reviewed-by: Ingo Molnar <[email protected]>
Reported-by: Michael Ellerman <[email protected]>	[2 build failures]
Reported-by: Fengguang Wu <[email protected]>	[2 build failures]
Reviewed-by: Andrew Morton <[email protected]>
Cc: Wei Yongjun <[email protected]>
Cc: Luis R. Rodriguez <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Mimi Zohar <[email protected]>
Cc: John Johansen <[email protected]>
Cc: Stephen Rothwell <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

kernel/ucount.c

@@ -10,6 +10,7 @@
 #include <linux/slab.h>
 #include <linux/cred.h>
 #include <linux/hash.h>
+#include <linux/kmemleak.h>
 #include <linux/user_namespace.h>
 
 #define UCOUNTS_HASHTABLE_BITS 10