perf tools: Add 'trace_fields' dynamic sort key

The 'trace_fields' sort key is similar as 'trace' sort key, but it shows
each fields separately.  Each event will get different columns as their
fields.

  $ perf report -s trace_fields --stdio
  # To display the perf.data header info, please use --header/--header-only options.
  #
  #
  # Total Lost Samples: 0
  #
  # Samples: 20K of event 'kmem:kmalloc'
  # Event count (approx.): 20533
  #
  # Overhead  Command           call_site                 ptr  bytes_req  bytes_alloc            gfp_flags
  # ........  .......  ..................  ..................  .........  ...........  ...................
  #
      99.89%  perf       ffffffffa01d4396  0xffff8803ffb79720         96           96    GFP_NOFS|GFP_ZERO
       0.06%  sleep      ffffffff8114e1cd  0xffff8803d228a000       4096         4096           GFP_KERNEL
       0.03%  perf       ffffffff811d6ae6  0xffff8803f7678f00        240          256  GFP_KERNEL|GFP_ZERO
       0.00%  perf       ffffffff812263c1  0xffff880406172380        128          128           GFP_KERNEL
       0.00%  perf       ffffffff812264b9  0xffff8803ffac1600        504          512           GFP_KERNEL
       0.00%  perf       ffffffff81226634  0xffff880401dc5280         28           32           GFP_KERNEL
       0.00%  sleep      ffffffff81226da9  0xffff8803ffac3a00        392          512           GFP_KERNEL

  # Samples: 20K of event 'kmem:kfree'
  # Event count (approx.): 20597
  #
  # Overhead           call_site                 ptr
  # ........  ..................  ..................
  #
      99.58%    ffffffffa01d85ad  0xffff8803ffb79720
       0.07%    ffffffff81443f5c  0xffff8803f7669400
       0.02%    ffffffff811d5753  0xffff8803f7678f00
       0.01%    ffffffff81443f5c  0xffff8803f766be00
       0.01%    ffffffff8114e359  0xffff8803d228a000
       0.01%    ffffffff81443f5c  0xffff8800d156dc00
       0.01%    ffffffff81443f5c  0xffff8803f7669400
       0.01%    ffffffff8114e359  0xffff8803d228a000
       0.01%    ffffffff8114e359  0xffff8803d228a000
       0.01%    ffffffff8114e359  0xffff8803d228a000

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1450804030-29193-13-git-send-email-namhyung@kernel.org
[ Combined with "perf tools: Fix segfault when using -s trace_fields" ]
Link: http://lkml.kernel.org/r/1451991518-25673-1-git-send-email-namhyung@kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>