blk-mq: allow changing of queue depth through sysfs

For request_fn based devices, the block layer exports a 'nr_requests'
file through sysfs to allow adjusting of queue depth on the fly.
Currently this returns -EINVAL for blk-mq, since it's not wired up.
Wire this up for blk-mq, so that it now also always dynamic
adjustments of the allowed queue depth for any given block device
managed by blk-mq.

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

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

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

diff --cc block/blk-mq-tag.h
Simple merge

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

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

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

diff --cc block/blk.h
Simple merge

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