perf top: Default to system wide using perf_target methods

Additionally we were not checking if a cpu list had been provided by the
user. Fix that.
Reported-by: David Ahern <dsahern@gmail.com>
Reported-by: Namhyung Kim <namhyung@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-ao3zrouylwmt7h9ikj0krubi@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-top.c

@@ -1270,8 +1270,7 @@ int cmd_top(int argc, const char **argv, const char *prefix __used)
 		goto out_delete_evlist;
 	}
 
-	if (top.target.tid == 0 && top.target.pid == 0 &&
-	    top.target.uid_str == NULL)
+	if (perf_target__none(&top.target))
 		top.target.system_wide = true;
 
 	if (perf_evlist__create_maps(top.evlist, &top.target) < 0)