Config.in: show kernel configuration menu only if ADK_TARGET_KERNEL_CUSTOMISING is set

Config.in

@@ -102,7 +102,7 @@ source "target/config/Config.in.runtime"
 endmenu
 
 menu "Kernel configuration"
-	visible if !ADK_CHOOSE_APPLIANCE
+	visible if !ADK_CHOOSE_APPLIANCE && ADK_TARGET_KERNEL_CUSTOMISING
 source "target/linux/Config.in"
 endmenu