mm: clean up mm_counter

Presently, per-mm statistics counter is defined by macro in sched.h

This patch modifies it to
  - defined in mm.h as inlinf functions
  - use array instead of macro's name creation.

This patch is for reducing patch size in future patch to modify
implementation of per-mm counter.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/fremap.c b/mm/fremap.c
index b6ec85a..46f5dac 100644
--- a/mm/fremap.c
+++ b/mm/fremap.c
@@ -40,7 +40,7 @@
 			page_remove_rmap(page);
 			page_cache_release(page);
 			update_hiwater_rss(mm);
-			dec_mm_counter(mm, file_rss);
+			dec_mm_counter(mm, MM_FILEPAGES);
 		}
 	} else {
 		if (!pte_file(pte))