block: continue ll_rw_blk.c splitup

Adds files for barrier handling, rq execution, io context handling,
mapping data to requests, and queue settings.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --cc block/Makefile
Simple merge

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

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

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

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

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

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

diff --cc block/blk.h
Simple merge