tests: Add missing kernels to system creation

Change 149c1fc2d070a8ce073263880ecf2ccf7535e569 removed the
default value of the kernels, and fs tests rely on those.

Change-Id: I6d83420af5881ab59c2d223a9915f363dd8a1c69
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18528
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.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.

mem: Allow read-only caches and check compliance

This patch adds a parameter to the BaseCache to enable a read-only
cache, for example for the instruction cache, or table-walker cache
(not for x86). A number of checks are put in place in the code to
ensure a read-only cache does not end up with dirty data.

A follow-on patch adds suitable read requests to allow a read-only
cache to explicitly ask for clean data.

config, x86: move kernel specification from tests to FSConfig.py

For some reason, the default x86 kernel is specified in
tests/configs/x86_generic.py and not in configs/common/FSConfig.py,
where the kernels for all the other ISAs are. This means that
running configs/example/fs.py for x86 fails because no kernel
is specified. Moving the specification over fixes this problem.

There is another problem that this uncovers, which is that going
past the init stage (i.e., past where the regression test stops)
fails because the fsck test on the disk device fails, but that's
a separate issue.

config: Move the memory instantiation outside FSConfig

This patch moves the instantiation of the memory controller outside
FSConfig and instead relies on the mem_ranges to pass the information
to the caller (e.g. fs.py or one of the regression scripts). The main
motivation for this change is to expose the structural composition of
the memory system and allow more tuning and configuration without
adding a large number of options to the makeSystem functions.

The patch updates the relevant example scripts to maintain the current
functionality. As the order that ports are connected to the memory bus
changes (in certain regresisons), some bus stats are shuffled
around. For example, what used to be layer 0 is now layer 1.

Going forward, options will be added to support the addition of
multi-channel memory controllers.

mem: More descriptive DRAM config names

This patch changes the class names of the variuos DRAM configurations
to better reflect what memory they are based on. The speed and
interface width is now part of the name, and also the alias that is
used to select them on the command line.

Some minor changes are done to the actual parameters, to better
reflect the named configurations. As a result of these changes the
regressions change slightly and the stats will be bumped in a separate
patch.

x86: regressions: add switcher full test

config: Add a mem-type config option to se/fs scripts

This patch enables selection of the memory controller class through a
mem-type command-line option. Behind the scenes, this option is
treated much like the cpu-type, and a similar framework is used to
resolve the valid options, and translate the short-hand description to
a valid class.

The regression scripts are updated with a hardcoded memory class for
the moment. The best solution going forward is probably to get the
memory out of the makeSystem functions, but Ruby complicates things as
it does not connect the memory controller to the membus.

tests: Create base classes to encapsulate common test configurations

Most of the test cases currently contain a large amount of duplicated
boiler plate code. This changeset introduces a set of classes that
encapsulates most of the functionality when setting up a test
configuration.

The following base classes are introduced:
* BaseSystem - Basic system configuration that can be used for both
SE and FS simulation.

* BaseFSSystem - Basic FS configuration uni-processor and multi-processor
configurations.

* BaseFSSystemUniprocessor - Basic FS configuration for uni-processor
configurations. This is provided as a way
to make existing test cases backwards
compatible.

Architecture specific implementations are provided for ARM, Alpha, and
X86.