Merge branch 'bcache-updates-6.19' into for-6.19/block

Merge bcache updates from Coly for 6.19:

"The major change is from me, which is to remove useless discard
 interface and code for cache device (not the backing device). And the
 last patch about gc latency is a cooperative result from Robert Pang
 (Google), Mingzhe Zou (Easystack) and me, by inspired from their
 previous works, I compose the final version and Robert prvides positive
 benchmark result.

 Marco contributes 2 patches to improve the usage of  per-cpu system
 work queue. Gustavo contributes a patch to fix the not-at-end
 flexible-array member warning by gcc14. And Qianfeng contributes a code
 cleanup patch to remove redundant __GFP_NOWARN."

Link: https://lore.kernel.org/linux-block/20251113053630.54218-1-colyli@fnnas.com/
Signed-off-by: Jens Axboe <axboe@kernel.dk>
* bcache-updates-6.19:
  bcache: Avoid -Wflex-array-member-not-at-end warning
  bcache: WQ_PERCPU added to alloc_workqueue users
  bcache: replace use of system_wq with system_percpu_wq
  bcache: remove redundant __GFP_NOWARN
  bcache: reduce gc latency by processing less nodes and sleep less time
  bcache: remove discard sysfs interface document
  bcache: drop discard sysfs interface
  bcache: remove discard code from alloc.c
  bcache: get rid of discard code from journal