blk-mq-debugfs: Add 'kick' operation

Running a queue causes the block layer to examine the per-CPU and
hw queues but not the requeue list. Hence add a 'kick' operation
that also examines the requeue list.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Eduardo Valentin <eduval@amazon.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>