mm: fix warnings regarding enum migrate_mode

sparc64 allmodconfig:

In file included from include/linux/compat.h:15,
from /usr/src/25/arch/sparc/include/asm/siginfo.h:19,
from include/linux/signal.h:5,
from include/linux/sched.h:73,
from arch/sparc/kernel/asm-offsets.c:13:
include/linux/fs.h:618: warning: parameter has incomplete type

It seems that my sparc64 compiler (gcc-3.4.5) doesn't like the forward
declaration of enums.

Fix this by moving the "enum migrate_mode" definition into its own header
file.

Acked-by: Mel Gorman <[e-mail]>
Cc: Rik van Riel <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Cc: Minchan Kim <[e-mail]>
Cc: Dave Jones <[e-mail]>
Cc: Jan Kara <[e-mail]>
Cc: Andy Isaacson <[e-mail]>
Cc: Nai Xia <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/fs.h

···
 #include <linux/ioctl.h>
 #include <linux/blk_types.h>
 #include <linux/types.h>
+#include <linux/migrate_mode.h>
 
 /*
  * It's silly to have NR_OPEN bigger than NR_FILE, but you can change
···
 struct page;
 struct address_space;
 struct writeback_control;
-enum migrate_mode;
 
 struct iov_iter {
 	const struct iovec *iov;

include/linux/migrate.h

···
 
 #include <linux/mm.h>
 #include <linux/mempolicy.h>
+#include <linux/migrate_mode.h>
 
 typedef struct page *new_page_t(struct page *, unsigned long private, int **);
-
-/*
- * MIGRATE_ASYNC means never block
- * MIGRATE_SYNC_LIGHT in the current implementation means to allow blocking
- *	on most operations but not ->writepage as the potential stall time
- *	is too significant
- * MIGRATE_SYNC will block when migrating pages
- */
-enum migrate_mode {
-	MIGRATE_ASYNC,
-	MIGRATE_SYNC_LIGHT,
-	MIGRATE_SYNC,
-};
 
 #ifdef CONFIG_MIGRATION
 #define PAGE_MIGRATION 1

include/linux/migrate_mode.h

···
+#ifndef MIGRATE_MODE_H_INCLUDED
+#define MIGRATE_MODE_H_INCLUDED
+/*
+ * MIGRATE_ASYNC means never block
+ * MIGRATE_SYNC_LIGHT in the current implementation means to allow blocking
+ *	on most operations but not ->writepage as the potential stall time
+ *	is too significant
+ * MIGRATE_SYNC will block when migrating pages
+ */
+enum migrate_mode {
+	MIGRATE_ASYNC,
+	MIGRATE_SYNC_LIGHT,
+	MIGRATE_SYNC,
+};
+
+#endif		/* MIGRATE_MODE_H_INCLUDED */