dm-crypt: use per-bio data

This patch changes 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 used
mempool for the allocation.

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
and allocated with the bio (using target per_bio_data_size option). If the
request needs additional values, they are allocated from the mempool.

CRs-fixed: 670391
Change-Id: I8abc48a021391398f3b35bdd4ac9efbbec3a9fa5
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Patch-mainline: dm-devel @ 04/05/14, 14:05
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>