perf header: Rename "sibling cores" to "sibling sockets"

The "sibling cores" actually shows the sibling CPUs of a socket.  The
name "sibling cores" is very misleading.

Rename "sibling cores" to "sibling sockets"
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1559688644-106558-4-git-send-email-kan.liang@linux.intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf.data-file-format.txt

@@ -168,7 +168,7 @@ struct {
 };
 
 Example:
-	sibling cores   : 0-8
+	sibling sockets : 0-8
 	sibling dies	: 0-3
 	sibling dies	: 4-7
 	sibling threads : 0-1

tools/perf/util/header.c

@@ -1460,7 +1460,7 @@ static void print_cpu_topology(struct feat_fd *ff, FILE *fp)
 	str = ph->env.sibling_cores;
 
 	for (i = 0; i < nr; i++) {
-		fprintf(fp, "# sibling cores   : %s\n", str);
+		fprintf(fp, "# sibling sockets : %s\n", str);
 		str += strlen(str) + 1;
 	}