configs: Fix Python 3 iterator and exec compatibility issues

Python 2.7 used to return lists for operations such as map and range,
this has changed in Python 3. To make the configs Python 3 compliant,
add explicit conversions from iterators to lists where needed, replace
xrange with range, and fix changes to exec syntax.

This change doesn't fix import paths since that might require us to
restructure the configs slightly.

Change-Id: Idcea8482b286779fc98b4e144ca8f54069c08024
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/16002
Reviewed-by: Gabe Black <gabeblack@google.com>

config: Refactor the network switch configuration file

This patch prevents the body of the script getting executed when
the script is imported as a module.

Change-Id: I70a50f6295f1e7a088398017f5fa9d06fe90476a
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>

config: Make configs/common a Python package

Continue along the same line as the recent patch that made the
Ruby-related config scripts Python packages and make also the
configs/common directory a package.

All affected config scripts are updated (hopefully).

Note that this change makes it apparent that the current organisation
and naming of the config directory and its subdirectories is rather
chaotic. We mix scripts that are directly invoked with scripts that
merely contain convenience functions. While it is not addressed in
this patch we should follow up with a re-organisation of the
config structure, and renaming of some of the packages.

dist: config file for distributed switch

Distributed gem5 is the result of the convergence effort between
multi-gem5 and pd-gem5. It relies on the base multi-gem5 infrastructure
for packet forwarding, synchronisation and checkpointing but combines
those with the elaborated network switch model from pd-gem5.