util/exynos: Port *_cksum.py to python3

BUG=chromium:1023662
TEST=1. Create a tiny file `in.txt` as input
     2. Run `fixed_cksum.py in.txt out.txt 20` with py2 and py3 version,
     the output is the same
     3. Run `variable_cksum.py in.txt out.txt` with py2 and py3 version,
     the output is the same

Signed-off-by: Yilin Yang <kerker@google.com>
Change-Id: I9428269dfb826a3a95fffef9ea3f7c1a7107ef84
Reviewed-on: https://review.coreboot.org/c/coreboot/+/45460
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>

util/exynos/fixed_cksum.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python3
 #
 # SPDX-License-Identifier: BSD-3-Clause
 
@@ -28,7 +28,7 @@ def main(argv):
     checksum_size = struct.calcsize(checksum_format)
     data_size = size - checksum_size
     assert len(data) <= data_size
-    checksum = struct.pack(checksum_format, sum(map(ord, data)))
+    checksum = struct.pack(checksum_format, sum(data))
     out_file.write(data + bytearray(data_size - len(data)) + checksum)