block: kill merge_bvec_fn() completely

As generic_make_request() is now able to handle arbitrarily sized bios,
it's no longer necessary for each individual block driver to define its
own ->merge_bvec_fn() callback. Remove every invocation completely.

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Lars Ellenberg <drbd-dev@lists.linbit.com>
Cc: drbd-user@lists.linbit.com
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Yehuda Sadeh <yehuda@inktank.com>
Cc: Sage Weil <sage@inktank.com>
Cc: Alex Elder <elder@kernel.org>
Cc: ceph-devel@vger.kernel.org
Cc: Alasdair Kergon <agk@redhat.com>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: dm-devel@redhat.com
Cc: Neil Brown <neilb@suse.de>
Cc: linux-raid@vger.kernel.org
Cc: Christoph Hellwig <hch@infradead.org>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Acked-by: NeilBrown <neilb@suse.de> (for the 'md' bits)
Acked-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
[dpark: also remove ->merge_bvec_fn() in dm-thin as well as
 dm-era-target, and resolve merge conflicts]
Signed-off-by: Dongsu Park <dpark@posteo.net>
Signed-off-by: Ming Lin <ming.l@ssi.samsung.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --cc block/blk-merge.c
Simple merge

diff --cc block/blk-settings.c
Simple merge

diff --cc drivers/block/drbd/drbd_int.h
Simple merge

diff --cc drivers/block/drbd/drbd_main.c
Simple merge

diff --cc drivers/block/drbd/drbd_req.c
Simple merge

diff --cc drivers/block/pktcdvd.c
Simple merge

diff --cc drivers/block/rbd.c
Simple merge

diff --cc drivers/md/dm-cache-target.c
Simple merge

diff --cc drivers/md/dm-crypt.c
Simple merge

diff --cc drivers/md/dm-era-target.c
Simple merge

diff --cc drivers/md/dm-flakey.c
Simple merge

diff --cc drivers/md/dm-linear.c
Simple merge

diff --cc drivers/md/dm-log-writes.c
Simple merge

diff --cc drivers/md/dm-raid.c
Simple merge

diff --cc drivers/md/dm-snap.c
Simple merge

diff --cc drivers/md/dm-stripe.c
Simple merge

diff --cc drivers/md/dm-table.c
Simple merge

diff --cc drivers/md/dm-thin.c
Simple merge

diff --cc drivers/md/dm-verity.c
Simple merge

diff --cc drivers/md/dm.c
Simple merge

diff --cc drivers/md/dm.h
Simple merge

diff --cc drivers/md/linear.c
Simple merge

diff --cc drivers/md/md.c
Simple merge

diff --cc drivers/md/md.h
Simple merge

diff --cc drivers/md/multipath.c
Simple merge

diff --cc drivers/md/raid0.c
Simple merge

diff --cc drivers/md/raid0.h
Simple merge

diff --cc drivers/md/raid1.c
Simple merge

diff --cc drivers/md/raid10.c
Simple merge

diff --cc drivers/md/raid5.c
Simple merge

diff --cc include/linux/blkdev.h
Simple merge

diff --cc include/linux/device-mapper.h
Simple merge