workqueue: add time-based panic for stalls

workqueue: add time-based panic for stalls

Add a new module parameter 'panic_on_stall_time' that triggers a panic
when a workqueue stall persists for longer than the specified duration
in seconds.

Unlike 'panic_on_stall' which counts accumulated stall events, this
parameter triggers based on the duration of a single continuous stall.
This is useful for catching truly stuck workqueues rather than
accumulating transient stalls.

Usage:
  workqueue.panic_on_stall_time=120

This would panic if any workqueue pool has been stalled for 120 seconds
or more.

The stall duration is measured from the workqueue last progress
(poll_ts) which accounts for legitimate system stalls.

Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Tejun Heo <tj@kernel.org>