New code for 5.4:
- Remove KM_SLEEP/KM_NOSLEEP.
- Ensure that memory buffers for IO are properly sector-aligned to avoid
  problems that the block layer doesn't check.
- Make the bmap scrubber more efficient in its record checking.
- Don't crash xfs_db when superblock inode geometry is corrupt.
- Fix btree key helper functions.
- Remove unneeded error returns for things that can't fail.
- Fix buffer logging bugs in repair.