perf thread_map: Change map entries into a struct

We need to store command names with the pid. Changing map entries to be
a struct holding pid. Process name is coming in shortly.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.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/1435012588-9007-2-git-send-email-jolsa@kernel.org
[ Split providing the set/get accessors from transforming the entries structs ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>