perf map: Optimize maps__fixup_overlappings()

perf map: Optimize maps__fixup_overlappings()

This function splits and removes overlapping areas.

Maps in tree are ordered by start address thus we could find first
overlap and stop if next map does not overlap.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/153365189407.435244.7234821822450484712.stgit@buzz
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>