perf tools: Protect accesses the map rbtrees with a rw lock

To allow concurrent access, next step: refcount struct map instances, so
that we can ditch maps->removed_maps and stop leaking threads, maps,
then struct DSO needs the same treatment.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-o45w2w5dzrza38nzqxnqzhyf@git.kernel.org


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