signrom: Rewrite as python script

Now that we have a hard dependency on python anyway, we can replace the
slow shell script to calculate the option ROM checksum with a fast AND
portable python version. Tested both with python 2.7 and 3.1.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

scripts/signrom.py

@@ -0,0 +1,40 @@
+#
+# Option ROM signing utility
+#
+# Authors:
+#  Jan Kiszka <jan.kiszka@siemens.com>
+#
+# This work is licensed under the terms of the GNU GPL, version 2 or later.
+# See the COPYING file in the top-level directory.
+
+import sys
+import struct
+
+if len(sys.argv) < 3:
+    print('usage: signrom.py input output')
+    sys.exit(1)
+
+fin = open(sys.argv[1], 'rb')
+fout = open(sys.argv[2], 'wb')
+
+fin.seek(2)
+size = ord(fin.read(1)) * 512 - 1
+
+fin.seek(0)
+data = fin.read(size)
+fout.write(data)
+
+checksum = 0
+for b in data:
+    # catch Python 2 vs. 3 differences
+    if isinstance(b, int):
+        checksum += b
+    else:
+        checksum += ord(b)
+checksum = (256 - checksum) % 256
+
+# Python 3 no longer allows chr(checksum)
+fout.write(struct.pack('B', checksum))
+
+fin.close()
+fout.close()