tracing: Convert some workqueue events to DEFINE_EVENT

Use DECLARE_EVENT_CLASS to remove duplicate code:

   text    data     bss     dec     hex filename
  13171     800      72   14043    36db kernel/workqueue.o.old
  12243     800      68   13111    3337 kernel/workqueue.o

Two events are converted:

  workqueue: workqueue_insertion, workqueue_execution

No change in functionality.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <4B0E289F.5010104@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>