perf tools: Introduce struct perf_target

The perf_target struct will be used for taking care of cpu/thread maps
based on user's input. Since it is used on various subcommands it'd
better factoring it out.

Thanks to Arnaldo for suggesting the better name.

Signed-off-by: Namhyung Kim <namhyung.kim@lge.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1335417327-11796-2-git-send-email-namhyung.kim@lge.com


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