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>

util: clean up attrdict and import multiattrdict into m5.util

multiattrdict: make multilevel nesting work properly

attrdict: add pickle support to attrdict

attrdict: correct delattr

python: Add a utility for nested attribute dicts.
Change attrdict so that attributes that begin with an underscore don't
go into the dict.

python: Move various utility classes into a new m5.util package so
they're all in the same place. This also involves having just one
jobfile.py and moving it into the utils directory to avoid
duplication. Lots of improvements to the utility as well.