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.
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