perf tools: Rename the 'single_dep' target to 'prepare'

And use the new 'prepare' target for the $(PERF_IN) target.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1443004442-32660-7-git-send-email-jolsa@kernel.org


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