stop passing a writeback_control to swap/shmem writeout v3

[Christoph Hellwig <hch@lst.de>]

Hi all,

this series was intended to remove the last remaining users of
AOP_WRITEPAGE_ACTIVATE after my other pending patches removed the
rest, but spectacularly failed at that.

But instead it nicely improves the code, and removes two pointers
from struct writeback_control.

Changes since v2:
 - fix up kerneldoc to not leave around the documentation for a removed
   parameter
 - add back the for_reclaim removal

Changes since v1:
 - drop to patch to be merged through a different tree or later
 - fix !CONFIG_SWAP compilation

Diffstat:
 drivers/gpu/drm/i915/gem/i915_gem_shmem.c |    3 -
 drivers/gpu/drm/ttm/ttm_backup.c          |    9 ---
 fs/fuse/file.c                            |   11 ---
 fs/nfs/write.c                            |    2 
 include/linux/shmem_fs.h                  |    5 +
 include/linux/writeback.h                 |   11 ---
 include/trace/events/btrfs.h              |    7 --
 include/trace/events/writeback.h          |    8 --
 mm/page_io.c                              |   71 +++++++++++--------------
 mm/shmem.c                                |   18 ++----
 mm/swap.h                                 |    9 ++-
 mm/vmscan.c                               |   84 +++++++++++++-----------------
 mm/zswap.c                                |    5 -
 13 files changed, 96 insertions(+), 147 deletions(-)