python: Replace DictMixin with Mapping / MutableMapping

Python 3 has removed support for DictMixin, so switch to Mapping /
MutableMapping in collections which provides the same functionality.

Change-Id: I61fbe366d2c9fc6e01b470f82f49cc02b99dec32
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/15984
Reviewed-by: Jason Lowe-Power <jason@lowepower.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>

python: Fix debug flag listing regression

The PyBind11 changes slightly modified gem5's internal debug
interfaces. The corresponding change to the public API went missing
before the new bindings were merged. This change updates the Python
glue to use the new interface.

Change-Id: I3ecca5a3f6c35b99d55126d697371124f81a12dd
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Matteo Andreozzi <matteo.andreozzi@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/3140
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

python: Move native wrappers to the _m5 namespace

Swig wrappers for native objects currently share the _m5.internal name
space with Python code. This is undesirable if we ever want to switch
from Swig to some other framework for native binding (e.g., PyBind11
or Boost::Python). This changeset moves all of such wrappers to the
_m5 namespace, which is now reserved for native code.

Change-Id: I2d2bc12dbc05b57b7c5a75f072e08124413d77f3
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

sim: Clarify the difference between tracing and debugging

This patch changes the name the command-line options related to debug
output to all start with "debug" rather than being a mix of that and
"trace". It also makes it clear that the breakpoint time is specified
in ticks and not in cycles.

debug: fix help output

trace: reimplement the DTRACE function so it doesn't use a vector
At the same time, rename the trace flags to debug flags since they
have broader usage than simply tracing. This means that
--trace-flags is now --debug-flags and --trace-help is now --debug-help

some new files are missing copyright notices

python: Try to isolate the stuff that's in the m5.internal package a bit more.