tools/perf/build: Flip Makefile.parallel and Makefile.perf

To make it more apparent that there is not change in functionality we introduced
Makefile.parallel separately and now flip it with the main Makefile, which
moves into Makefile.perf.

The renames are:

   Makefile.parallel => Makefile
   Makefile          => Makefile.perf

Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/n/tip-igRfuw9ugbnnpixLd6wpptzl@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>