scsi: scsi-mq-debugfs: Show more information

Show the request result, request timeout and SCSI command flags.  This
information is very helpful when trying to figure out why a queue got
stuck. An example of the information that is exported through debugfs:

$ (cd /sys/kernel/debug/block && find -type f -print0 | xargs -0 grep ago)
./sda/hctx0/busy:ffff8804a4523300 {.op=READ, .cmd_flags=FAILFAST_DEV|FAILFAST_TRANSPORT|FAILFAST_DRIVER|RAHEAD, .rq_flags=MQ_INFLIGHT|DONTPREP|IO_STAT|STATS, .atomic_flags=STARTED, .tag=24, .internal_tag=-1, .cmd=Read(10) 28 00 06 80 1c c8 00 00 08 00, .retries=0, .result = 0x0, .flags=TAGGED|INITIALIZED, .timeout=90.000, allocated 0.010 s ago}

Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: James E.J. Bottomley <jejb@linux.vnet.ibm.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>