xfs, iomap: update for 4.8-rc3

Changes in this update
- regression fixes for XFS changes introduce in 4.8-rc1
	- buffer IO accounting assert failure
	- ENOSPC block accounting reservation issue
	- DAX IO path page cache invalidation fix
	- rmapbt on-disk block count in agf
	- correct classification of rmap block type when updating AGFL.
	- iomap support for attribute fork mapping
- regression fixes for iomap infrastructure in 4.8-rc1
	- fiemap: honor FIEMAP_FLAG_SYNC
	- fiemap: implement FIEMAP_FLAG_XATTR support to fix XFS regression
	- make mark_page_accessed and pagefault_disable usage consistent with
	  other IO paths
Merge branch 'iomap-fixes-4.8-rc3' into for-next