perf mem: Add -e record option

Adding -e option for perf mem record command, to be able to specify
memory event directly.

Get list of available events:

  $ perf mem record -e list
  ldlat-loads
  ldlat-stores

Monitor ldlat-loads:
  $ perf mem record -e ldlat-loads true

Committer notes:

Further testing:

  # perf mem record -e ldlat-loads true
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.020 MB perf.data (10 samples) ]
  # perf evlist
  cpu/mem-loads,ldlat=30/P
  #

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1455525293-8671-6-git-send-email-jolsa@kernel.org


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