python: Don't assume SimObjects live in the global namespace

The importer in Python 3 doesn't like the way we import SimObjects
from the global namespace. Convert the existing SimObject declarations
to import from m5.objects. As a side-effect, this makes these files
consistent with configuration files.

Change-Id: I11153502b430822130722839e1fa767b82a027aa
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/15981
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>

cpu: Make checker CPUs inherit from CheckerCPU in the Python hierarchy

Checker CPUs currently don't inherit from the CheckerCPU in the Python
object hierarchy. This has two consequences:
* It makes CPU model discovery from the Python world somewhat
complicated as there is no way of testing if a CPU is a checker.
* Parameters are duplicated in the checker configuration
specification.

This changeset makes all checker CPUs inherit from the base checker
CPU class.

cpu: Add header files for checker CPUs

In order to create reliable SWIG wrappers, we need to include the
declaration of the wrapped class in the SWIG file. Previously, we
didn't expose the declaration of checker CPUs. This patch adds header
files for such CPUs and include them in the SWIG wrapper.

CPU: Remove overloaded function_trace_start parameter

This patch removes the overloading of the parameter, which seems both
redundant, and possibly incorrect.

The inorder CPU is particularly interesting as it uses a different
name for the parameter, and never make any use of it internally.

CheckerCPU: Re-factor CheckerCPU to be compatible with current gem5

Brings the CheckerCPU back to life to allow FS and SE checking of the
O3CPU. These changes have only been tested with the ARM ISA. Other
ISAs potentially require modification.

python: Move more code into m5.util allow SCons to use that code.
Get rid of misc.py and just stick misc things in __init__.py
Move utility functions out of SCons files and into m5.util
Move utility type stuff from m5/__init__.py to m5/util/__init__.py
Remove buildEnv from m5 and allow access only from m5.defines
Rename AddToPath to addToPath while we're moving it to m5.util
Rename read_command to readCommand while we're moving it
Rename compare_versions to compareVersions while we're moving it.

Changed BaseCPU::ProfileEvent's interval member to be of type Tick. This was done to be consistent with its
python type of a latency. In addition, the multiple definitions of profile in the different cpu models caused
problems for intialization of the interval value. If a child class's profile value was defined, the parent
BaseCPU::ProfileEvent interval field would be initialized with a garbage value. The fix was to remove the
multiple redifitions of profile in the child CPU classes.

Move SimObject python files alongside the C++ and fix
the SConscript files so that only the objects that are
actually available in a given build are compiled in.
Remove a bunch of files that aren't used anymore.