hung_task: dump blocker task if it is not hung

Dump the lock blocker task if it is not hung because if the blocker task
is also hung, it should be dumped by the detector.  This will de-duplicate
the same stackdumps if the blocker task is also blocked by another task
(and hung).

Link: https://lkml.kernel.org/r/175391351423.688839.11917911323784986774.stgit@devnote2


Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Suggested-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Tested-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Lance Yang <lance.yang@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>