perf tools: Share map_groups among threads of the same group

Sharing map groups within all process threads. This way
there's only one copy of mmap info and it's reachable
from any thread within the process.

Original-patch-by: Arnaldo Carvalho de Melo <acme@kernel.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1397490723-1992-5-git-send-email-jolsa@redhat.com
Signed-off-by: Jiri Olsa <jolsa@kernel.org>