volume_id: Adopt to new config style.

Config instructions for util-linux/volume_id are moved into the
source files according to the new config feature.

No code change.

Signed-off-by: Sven-Göran Bergh <sgb@systemasis.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/util-linux/volume_id/unused_mac.c b/util-linux/volume_id/unused_mac.c
index 5c40532..a1a53d1 100644
--- a/util-linux/volume_id/unused_mac.c
+++ b/util-linux/volume_id/unused_mac.c
@@ -20,6 +20,15 @@
 
 //kbuild:### lib-$(CONFIG_FEATURE_VOLUMEID_MAC) += mac.o
 
+//config:
+//config:### config FEATURE_VOLUMEID_MAC
+//config:###	bool "mac filesystem"
+//config:###	default y
+//config:###	depends on VOLUMEID
+//config:###	help
+//config:###	  TODO
+//config:
+
 #include "volume_id_internal.h"
 
 struct mac_driver_desc {