f2fs: add missing version info in superblock

The mkfs.f2fs remains kernel version in superblock, but f2fs module has not
added that so far.
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

include/linux/f2fs_fs.h

@@ -50,6 +50,8 @@
 #define MAX_ACTIVE_NODE_LOGS	8
 #define MAX_ACTIVE_DATA_LOGS	8
 
+#define VERSION_LEN	256
+
 /*
  * For superblock
  */
@@ -86,6 +88,9 @@ struct f2fs_super_block {
 	__le32 extension_count;		/* # of extensions below */
 	__u8 extension_list[F2FS_MAX_EXTENSION][8];	/* extension array */
 	__le32 cp_payload;
+	__u8 version[VERSION_LEN];	/* the kernel version */
+	__u8 init_version[VERSION_LEN];	/* the initial kernel version */
+	__u8 reserved[892];		/* valid reserved region */
 } __packed;
 
 /*