blk-mq: ensure that hardware queues are always run on the mapped CPUs

Instead of providing soft mappings with no guarantees on hardware
queues always being run on the right CPU, switch to a hard mapping
guarantee that ensure that we always run the hardware queue on
(one of, if more) the mapped CPU.

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

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

diff --cc include/linux/blk-mq.h
Simple merge