xfs: update for 4.8-rc1 Changes in this update: o generic iomap based IO path infrastructure o generic iomap based fiemap implementation o xfs iomap based Io path implementation o buffer error handling fixes o tracking of in flight buffer IO for unmount serialisation o direct IO and DAX io path separation and simplification o shortform directory format definition changes for wider platform compatibility o various buffer cache fixes o cleanups in preparation for rmap merge o error injection cleanups and fixes o log item format buffer memory allocation restructuring to prevent rare OOM reclaim deadlocks o sparse inode chunks are now fully supported.