xfs: move xfs_bmbt_irec and xfs_exntst_t to xfs_types.h

Neither defines an on-disk format, so move them out of xfs_format.h.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>