perf tools: Introduce 'P' modifier to request max precision

The 'P' will cause the event to get maximum possible detected precise
level.

Following record:
  $ perf record -e cycles:P ...

will detect maximum precise level for 'cycles' event and use it.

Commiter note:

Testing it:

  $ perf record -e cycles:P usleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.013 MB perf.data (9 samples) ]
  $ perf evlist
  cycles:P
  $ perf evlist -v
  cycles:P: size: 112, { sample_period, sample_freq }: 4000, sample_type:
  IP|TID|TIME|PERIOD, disabled: 1, inherit: 1, mmap: 1, comm: 1, freq: 1,
  enable_on_exec: 1, task: 1, precise_ip: 2, sample_id_all: 1, mmap2: 1,
  comm_exec: 1
  $

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1444068369-20978-6-git-send-email-jolsa@kernel.org


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