perf kmem: Print gfp flags in human readable string

Save libtraceevent output and print it in the header.

  # perf kmem stat --page --caller
  #
  # GFP flags
  # ---------
  # 00000010:       NI: GFP_NOIO
  # 000000d0:        K: GFP_KERNEL
  # 00000200:      NWR: GFP_NOWARN
  # 000084d0:    K|R|Z: GFP_KERNEL|GFP_REPEAT|GFP_ZERO
  # 000200d2:       HU: GFP_HIGHUSER
  # 000200da:      HUM: GFP_HIGHUSER_MOVABLE
  # 000280da:    HUM|Z: GFP_HIGHUSER_MOVABLE|GFP_ZERO
  # 002084d0: K|R|Z|NT: GFP_KERNEL|GFP_REPEAT|GFP_ZERO|GFP_NOTRACK
  # 0102005a:  NF|HW|M: GFP_NOFS|GFP_HARDWALL|GFP_MOVABLE

  ---------------------------------------------------------------------------------------------------------
   Total alloc (KB) | Hits      | Order | Mig.type | GFP flags | Callsite
  ---------------------------------------------------------------------------------------------------------
                 60 |        15 |     0 | UNMOVABL | K|R|Z|NT  | pte_alloc_one
                 40 |        10 |     0 |  MOVABLE | HUM|Z     | handle_mm_fault
                 24 |         6 |     0 |  MOVABLE | HUM       | do_wp_page
                 24 |         6 |     0 | UNMOVABL | K         | __pollwait
   ...

Requested-by: Joonsoo Kim <js1304@gmail.com>
Suggested-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Pekka Enberg <penberg@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/1429592107-1807-5-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>