perf tools: Make numa benchmark optional

Commit "perf: Add 'perf bench numa mem'..." added a NUMA performance
benchmark to perf. Make this optional and test for required
dependencies.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1359337882-21821-1-git-send-email-peter@hurleysoftware.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>