use DECLARE_EVENT_CLASS to remove duplicate code:

   text    data     bss     dec     hex filename
  53570    3284     184   57038    dece block/blk-core.o.old
  43702    3284     144   47130    b81a block/blk-core.o

12 events are converted:

  block_rq: block_rq_insert, block_rq_issue
  block_rq_with_error: block_rq_{abort, requeue, complete}
  block_bio: block_bio_{backmerge, frontmerge, queue}
  block_get_rq: block_getrq, block_sleeprq
  block_unplug: block_unplug_timer, block_unplug_io

No change in functionality.
Signed-off-by: NLi Zefan <lizf@cn.fujitsu.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <4B0E28E6.7060609@cn.fujitsu.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>