f2fs: large volume support

f2fs's cp has one page which consists of struct f2fs_checkpoint and
version bitmap of sit and nat. To support lots of segments, we need more
blocks for sit bitmap. So let's arrange sit bitmap as following:
+-----------------+------------+
| f2fs_checkpoint | sit bitmap |
| + nat bitmap    |            |
+-----------------+------------+
0                 4k        N blocks

Signed-off-by: Changman Lee <cm224.lee@samsung.com>
[Jaegeuk Kim: simple code change for readability]
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/include/linux/f2fs_fs.h b/include/linux/f2fs_fs.h
index ba6f312..6ff0b0b 100644
--- a/include/linux/f2fs_fs.h
+++ b/include/linux/f2fs_fs.h
@@ -19,6 +19,7 @@
 #define F2FS_LOG_SECTORS_PER_BLOCK	3	/* 4KB: F2FS_BLKSIZE */
 #define F2FS_BLKSIZE			4096	/* support only 4KB block */
 #define F2FS_MAX_EXTENSION		64	/* # of extension entries */
+#define F2FS_BLK_ALIGN(x)	(((x) + F2FS_BLKSIZE - 1) / F2FS_BLKSIZE)
 
 #define NULL_ADDR		((block_t)0)	/* used as block_t addresses */
 #define NEW_ADDR		((block_t)-1)	/* used as block_t addresses */
@@ -75,6 +76,7 @@
 	__le16 volume_name[512];	/* volume name */
 	__le32 extension_count;		/* # of extensions below */
 	__u8 extension_list[F2FS_MAX_EXTENSION][8];	/* extension array */
+	__le32 cp_payload;
 } __packed;
 
 /*