xfs: add sparse inode chunk alignment superblock field

Add sb_spino_align to the superblock to specify sparse inode chunk
alignment. This also currently represents the minimum allowable sparse
chunk allocation size.

Signed-off-by: Brian Foster <bfoster@redhat.com>

diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
index 4daaa66..899d6b4 100644
--- a/fs/xfs/libxfs/xfs_format.h
+++ b/fs/xfs/libxfs/xfs_format.h
@@ -170,7 +170,7 @@
 	__uint32_t	sb_features_log_incompat;
 
 	__uint32_t	sb_crc;		/* superblock crc */
-	__uint32_t	sb_pad;
+	xfs_extlen_t	sb_spino_align;	/* sparse inode chunk alignment */
 
 	xfs_ino_t	sb_pquotino;	/* project quota inode */
 	xfs_lsn_t	sb_lsn;		/* last write sequence */
@@ -256,7 +256,7 @@
 	__be32		sb_features_log_incompat;
 
 	__le32		sb_crc;		/* superblock crc */
-	__be32		sb_pad;
+	__be32		sb_spino_align;	/* sparse inode chunk alignment */
 
 	__be64		sb_pquotino;	/* project quota inode */
 	__be64		sb_lsn;		/* last write sequence */