util: Port util to python3

This commit is the result of running 2to3 converter on the util
subdirectory

JIRA: https://gem5.atlassian.net/browse/GEM5-832

Change-Id: I4e7e2d2b1b99f7bcc5fe0f6dc5d25880323616eb
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/37797
Reviewed-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

util/protolib.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2.7
+#!/usr/bin/env python3
 
 # Copyright (c) 2013 ARM Limited
 # All rights reserved
@@ -91,7 +91,7 @@ def openFileRd(in_file):
         except IOError:
             proto_in = open(in_file, 'rb')
     except IOError:
-        print "Failed to open ", in_file, " for reading"
+        print("Failed to open ", in_file, " for reading")
         exit(-1)
     return proto_in