Add a helper script to add a DFU header

This is so simple we can do it in 10 lines of Python. It matches the format of
the `add_capsule_header.py` utility.

contrib/firmware_packager/add_dfu_header.py

@@ -0,0 +1,49 @@
+#!/usr/bin/python3
+# -*- coding: utf-8 -*-
+#
+# Copyright (C) 2020 Richard Hughes <richard@hughsie.com>
+#
+# SPDX-License-Identifier: LGPL-2.1+
+
+import struct
+import zlib
+import argparse
+
+def main(bin_fn, dfu_fn, pad, vid, pid, rev):
+
+    # read binary file
+    with open(bin_fn, 'rb') as f:
+        blob = f.read()
+
+    # pad blob to a specific size
+    if pad:
+        while len(blob) < int(pad, 16):
+            blob += b'\0'
+
+    # create DFU footer with checksum
+    blob += struct.pack('<HHHH3sB',
+                        int(rev, 16),   # version
+                        int(pid, 16),   # PID
+                        int(vid, 16),   # VID
+                        0x0100,         # DFU version
+                        b'UFD',         # signature
+                        0x10)           # hdrlen
+    crc32 = zlib.crc32(blob) ^ 0xffffffff
+    blob += struct.pack('<L', crc32)
+
+    # write binary file
+    with open(dfu_fn, 'wb') as f:
+        f.write(blob)
+
+if __name__ == "__main__":
+
+    # parse args
+    parser = argparse.ArgumentParser(description='Add DFU footer on firmware')
+    parser.add_argument('--bin', help='Path to the .bin file', required=True)
+    parser.add_argument('--dfu', help='Output DFU file path', required=True)
+    parser.add_argument('--pad', help='Pad to a specific size, e.g. 0x4000', default=None)
+    parser.add_argument('--vid', help='Vendor ID, e.g. 0x273f', required=True)
+    parser.add_argument('--pid', help='Product ID, e.g. 0x1002', required=True)
+    parser.add_argument('--rev', help='Revision, e.g. 0x1000', required=True)
+    args = parser.parse_args()
+    main(args.bin, args.dfu, args.pad, args.vid, args.pid, args.rev)