dm crypt: use per-bio data

dm crypt: use per-bio data

Change dm-crypt so that it uses auxiliary data allocated with the bio.

Dm-crypt requires two allocations per request - struct dm_crypt_io and
struct ablkcipher_request (with other data appended to it).  It
previously only used mempool allocations.

Some requests may require more dm_crypt_ios and ablkcipher_requests,
however most requests need just one of each of these two structures to
complete.

This patch changes it so that the first dm_crypt_io and ablkcipher_request
are allocated with the bio (using target per_bio_data_size option).  If
the request needs additional values, they are allocated from the mempool.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
(cherry picked from commit 298a9fa08a1577211d42a75e8fc073baef61e0d9)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
 Conflicts:
	drivers/md/dm-crypt.c
 Solutions:
	reuse the old bio->sector instead of bvec ioterator