ubifs: Import atomic_long operations from Linux

This commit is a preperation for a subsequent UBIFS commit
which needs atomic_long operations.

Therefor "include/asm-generic/atomic-long.h" is imported
from 1860e37 Linux 3.15

Signed-off-by: Anton Habegger <anton.habegger@gmail.com>
diff --git a/fs/ubifs/ubifs.h b/fs/ubifs/ubifs.h
index c120261..a51b237 100644
--- a/fs/ubifs/ubifs.h
+++ b/fs/ubifs/ubifs.h
@@ -31,6 +31,8 @@
 #include <linux/backing-dev.h>
 #include "ubifs-media.h"
 #else
+#include <asm/atomic.h>
+#include <asm-generic/atomic-long.h>
 #include <ubi_uboot.h>
 
 #include <linux/ctype.h>
@@ -63,16 +65,6 @@
 
 void iput(struct inode *inode);
 
-/*
- * The atomic operations are used for budgeting etc which is not
- * needed for the read-only U-Boot implementation:
- */
-#define atomic_long_inc(a)
-#define atomic_long_dec(a)
-#define	atomic_long_sub(a, b)
-
-typedef unsigned long atomic_long_t;
-
 /* linux/include/time.h */
 #define NSEC_PER_SEC	1000000000L
 #define get_seconds()	0