Add trace_iomap_dio_rw_begin, trace_iomap_dio_rw_queued and
trace_iomap_dio_complete tracepoint.
trace_iomap_dio_rw_queued is mostly only to know that the request was
queued and -EIOCBQUEUED was returned. It is mostly trace_iomap_dio_rw_begin
& trace_iomap_dio_complete which has all the details.

<example output log>
      a.out-2073  [006]   134.225717: iomap_dio_rw_begin:   dev 7:7 ino 0xe size 0x0 offset 0x0 length 0x1000 done_before 0x0 flags DIRECT|WRITE dio_flags DIO_FORCE_WAIT aio 1
      a.out-2073  [006]   134.226234: iomap_dio_complete:   dev 7:7 ino 0xe size 0x1000 offset 0x1000 flags DIRECT|WRITE aio 1 error 0 ret 4096
      a.out-2074  [006]   136.225975: iomap_dio_rw_begin:   dev 7:7 ino 0xe size 0x1000 offset 0x0 length 0x1000 done_before 0x0 flags DIRECT dio_flags  aio 1
      a.out-2074  [006]   136.226173: iomap_dio_rw_queued:  dev 7:7 ino 0xe size 0x1000 offset 0x1000 length 0x0
ksoftirqd/3-31    [003]   136.226389: iomap_dio_complete:   dev 7:7 ino 0xe size 0x1000 offset 0x1000 flags DIRECT aio 1 error 0 ret 4096
      a.out-2075  [003]   141.674969: iomap_dio_rw_begin:   dev 7:7 ino 0xe size 0x1000 offset 0x0 length 0x1000 done_before 0x0 flags DIRECT|WRITE dio_flags  aio 1
      a.out-2075  [003]   141.676085: iomap_dio_rw_queued:  dev 7:7 ino 0xe size 0x1000 offset 0x1000 length 0x0
kworker/2:0-27    [002]   141.676432: iomap_dio_complete:   dev 7:7 ino 0xe size 0x1000 offset 0x1000 flags DIRECT|WRITE aio 1 error 0 ret 4096
      a.out-2077  [006]   143.443746: iomap_dio_rw_begin:   dev 7:7 ino 0xe size 0x1000 offset 0x0 length 0x1000 done_before 0x0 flags DIRECT dio_flags  aio 1
      a.out-2077  [006]   143.443866: iomap_dio_rw_queued:  dev 7:7 ino 0xe size 0x1000 offset 0x1000 length 0x0
ksoftirqd/5-41    [005]   143.444134: iomap_dio_complete:   dev 7:7 ino 0xe size 0x1000 offset 0x1000 flags DIRECT aio 1 error 0 ret 4096
      a.out-2078  [007]   146.716833: iomap_dio_rw_begin:   dev 7:7 ino 0xe size 0x1000 offset 0x0 length 0x1000 done_before 0x0 flags DIRECT dio_flags  aio 0
      a.out-2078  [007]   146.717639: iomap_dio_complete:   dev 7:7 ino 0xe size 0x1000 offset 0x1000 flags DIRECT aio 0 error 0 ret 4096
      a.out-2079  [006]   148.972605: iomap_dio_rw_begin:   dev 7:7 ino 0xe size 0x1000 offset 0x0 length 0x1000 done_before 0x0 flags DIRECT dio_flags  aio 0
      a.out-2079  [006]   148.973099: iomap_dio_complete:   dev 7:7 ino 0xe size 0x1000 offset 0x1000 flags DIRECT aio 0 error 0 ret 4096
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
[djwong: line up strings all prettylike]
Signed-off-by: Darrick J. Wong <djwong@kernel.org>