nvmet: replace use of system_wq with system_percpu_wq

This patch continues the effort to refactor workqueue APIs, which has begun
with the changes introducing new workqueues and a new alloc_workqueue flag:

   commit 128ea9f ("workqueue: Add system_percpu_wq and system_dfl_wq")
   commit 930c2ea ("workqueue: Add new WQ_PERCPU flag")

The point of the refactoring is to eventually alter the default behavior of
workqueues to become unbound by default so that their workload placement is
optimized by the scheduler.

Before that to happen, workqueue users must be converted to the better named
new workqueues with no intended behaviour changes:

   system_wq -> system_percpu_wq
   system_unbound_wq -> system_dfl_wq

This way the old obsolete workqueues (system_wq, system_unbound_wq) can be
removed in the future.

Link: https://lore.kernel.org/all/[email protected]/
Suggested-by: Tejun Heo <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Marco Crivellari <[email protected]>
Signed-off-by: Keith Busch <[email protected]>

Author: DispatchCode

drivers/nvme/target/admin-cmd.c

@@ -1605,7 +1605,7 @@ void nvmet_execute_keep_alive(struct nvmet_req *req)
 
 	pr_debug("ctrl %d update keep-alive timer for %d secs\n",
 		ctrl->cntlid, ctrl->kato);
-	mod_delayed_work(system_wq, &ctrl->ka_work, ctrl->kato * HZ);
+	mod_delayed_work(system_percpu_wq, &ctrl->ka_work, ctrl->kato * HZ);
 out:
 	nvmet_req_complete(req, status);
 }

drivers/nvme/target/fabrics-cmd-auth.c

@@ -390,7 +390,7 @@ void nvmet_execute_auth_send(struct nvmet_req *req)
 	    req->sq->dhchap_step != NVME_AUTH_DHCHAP_MESSAGE_FAILURE2) {
 		unsigned long auth_expire_secs = ctrl->kato ? ctrl->kato : 120;
 
-		mod_delayed_work(system_wq, &req->sq->auth_expired_work,
+		mod_delayed_work(system_percpu_wq, &req->sq->auth_expired_work,
 				 auth_expire_secs * HZ);
 		goto complete;
 	}