kconfig: Do not print status messages in make -s mode

Add an -s option to the various frontends and pass it when make -s is
used. Also, use $(kecho) instead of @echo in the Makefile.

Signed-off-by: Michal Marek <mmarek@suse.cz>
diff --git a/scripts/kconfig/gconf.c b/scripts/kconfig/gconf.c
index 344b9e3..26d208b 100644
--- a/scripts/kconfig/gconf.c
+++ b/scripts/kconfig/gconf.c
@@ -1474,9 +1474,12 @@
 		case 'a':
 			//showAll = 1;
 			break;
+		case 's':
+			conf_set_message_callback(NULL);
+			break;
 		case 'h':
 		case '?':
-			printf("%s <config>\n", av[0]);
+			printf("%s [-s] <config>\n", av[0]);
 			exit(0);
 		}
 		name = av[2];