perf tools: Introduce perf_target__validate() helper

perf tools: Introduce perf_target__validate() helper

The perf_target__validate function is used to check given PID/TID/UID/CPU
target options and warn if some combination is impossible. Also this can
make some arguments of parse_target_uid() function useless as it is checked
before the call via our new helper.

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/1335417327-11796-5-git-send-email-namhyung.kim@lge.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>