[PATCHSET v5 0/4] Add support for list issue

[Jens Axboe]

Hi,

With the support in 5.16-rc1 for allocating and completing batches of
IO, the one missing piece is passing down a list of requests for issue.
Drivers can take advantage of this by defining an mq_ops->queue_rqs()
hook.

This implements it for NVMe, allowing copy of multiple commands in one
swoop.

This is good for around a 500K IOPS/core improvement in my testing,
which is around a 5-6% improvement in efficiency.

Note to Christoph - I kept the copy helper, since it's used in 3
spots and I _think_ you ended up being fine with that...

Changes since v4:
- Get rid of nvme_submit_cmd()
- Check for prev == NULL for batched issue