qapi: Streamline boilerplate comment generation

Every generator has separate boilerplate for .h and .c, and their
differences are boring.  All of them repeat the license note.

Reduce the repetition as follows.  Move common text like the license
note to common open_output(), next to the existing common text there.
For each generator, replace the two separate descriptions by a single
one.

While there, emit an "automatically generated" note into generated
documentation, too.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20180211093607.27351-3-armbru@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

scripts/qapi-types.py

@@ -250,39 +250,19 @@ for o, a in opts:
     if o in ('-b', '--builtins'):
         do_builtins = True
 
-c_comment = '''
-/*
- * deallocation functions for schema-defined QAPI types
+blurb = '''
+ * Schema-defined QAPI types
  *
  * Copyright IBM, Corp. 2011
  *
  * Authors:
  *  Anthony Liguori   <aliguori@us.ibm.com>
  *  Michael Roth      <mdroth@linux.vnet.ibm.com>
- *
- * This work is licensed under the terms of the GNU LGPL, version 2.1 or later.
- * See the COPYING.LIB file in the top-level directory.
- *
- */
-'''
-h_comment = '''
-/*
- * schema-defined QAPI types
- *
- * Copyright IBM, Corp. 2011
- *
- * Authors:
- *  Anthony Liguori   <aliguori@us.ibm.com>
- *
- * This work is licensed under the terms of the GNU LGPL, version 2.1 or later.
- * See the COPYING.LIB file in the top-level directory.
- *
- */
 '''
 
 (fdef, fdecl) = open_output(output_dir, do_c, do_h, prefix,
                             'qapi-types.c', 'qapi-types.h',
-                            c_comment, h_comment)
+                            blurb)
 
 fdef.write(mcgen('''
 #include "qemu/osdep.h"