nvme-auth: use workqueue dedicated to authentication

NVMe In-Band authentication uses two kinds of works: chap->auth_work and
ctrl->dhchap_auth_work. The latter work flushes or cancels the former
work. However, the both works are queued to the same workqueue nvme-wq.
It results in the lockdep WARNING as follows:

 WARNING: possible recursive locking detected
 6.2.0-rc4+ #1 Not tainted
 --------------------------------------------
 kworker/u16:7/69 is trying to acquire lock:
 ffff902d52e65548 ((wq_completion)nvme-wq){+.+.}-{0:0}, at: start_flush_work+0x2c5/0x380

 but task is already holding lock:
 ffff902d52e65548 ((wq_completion)nvme-wq){+.+.}-{0:0}, at: process_one_work+0x210/0x410

To avoid the WARNING, introduce a new workqueue nvme-auth-wq dedicated
to chap->auth_work.

Reported-by: Daniel Wagner <dwagner@suse.de>
Link: https://lore.kernel.org/linux-nvme/20230130110802.paafkiipmitwtnwr@carbon.lan/


Fixes: f50fff73 ("nvme: implement In-Band authentication")
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Tested-by: Daniel Wagner <dwagner@suse.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>