python: Enforce absolute imports for Python 3 compatibility

Change-Id: Ia88d7fd472f7aed9b97df81468211384981bf6c6
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/15983
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

src/python/m5/ext/__init__.py

@@ -36,3 +36,6 @@
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #
 # Authors: Glenn Bergmans
+
+from __future__ import print_function
+from __future__ import absolute_import

src/python/m5/ext/pyfdt/pyfdt.py

@@ -19,6 +19,9 @@ Device Tree Blob Parser
 @author: Neil 'superna' Armstrong <superna9999@gmail.com>
 """
 
+from __future__ import print_function
+from __future__ import absolute_import
+
 import string
 import os
 import json