greybus: update a few header file comments

Add a GPLv2 tag and reword some comments at the top of "greybus_desc.h"
and "svc_msg.h".
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

drivers/staging/greybus/greybus_manifest.h

 /*
- * Greybus device descriptor definition
+ * Greybus module manifest definition
  *
- * Defined in the "Greybus Application Protocol" document.
- * See that document for any details on these values and structures.
+ * See "Greybus Application Protocol" document (version 0.draft) for
+ * details on these values and structures.
  *
  * Copyright 2014 Google Inc.
+ *
+ * Released under the GPLv2 only.
  */
 
 #ifndef __GREYBUS_DESC_H

drivers/staging/greybus/svc_msg.h

 /*
  * Greybus AP <-> SVC message structure format.
  *
- * Defined in the "Greybus Application Protocol" document.
- * See that document for any details on these values and structures.
+ * See "Greybus Application Protocol" document (version 0.draft) for
+ * details on these values and structures.
  *
  * Copyright 2014 Google Inc.
+ *
+ * Released under the GPLv2 only.
  */
 
 #ifndef __SVC_MSG_H