python: Stop using basestring to test for strings

The base class basestring doesn't exist in Python 3. Use string_types
from six instead.

Change-Id: I7e84903fb7dd4a0af7ae4e9f4ec2e54338f212bb
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/15998
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Juha Jäykkä <juha.jaykka@arm.com>

scons: Switch from the print statement to the print function.

Starting with version 3, scons imposes using the print function instead
of the print statement in code it processes. To get things building
again, this change moves all python code within gem5 to use the
function version. Another change by another author separately made this
same change to the site_tools and site_init.py files.

Change-Id: I2de7dc3b1be756baad6f60574c47c8b7e80ea3b0
Reviewed-on: https://gem5-review.googlesource.com/8761
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>

slicc: cleanup slicc code and make it less verbose

slicc: Pure python implementation of slicc.
This is simply a translation of the C++ slicc into python with very minimal
reorganization of the code. The output can be verified as nearly identical
by doing a "diff -wBur".

Slicc can easily be run manually by using util/slicc