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>

sim: Include object header files in SWIG interfaces

When casting objects in the generated SWIG interfaces, SWIG uses
classical C-style casts ( (Foo *)bar; ). In some cases, this can
degenerate into the equivalent of a reinterpret_cast (mainly if only a
forward declaration of the type is available). This usually works for
most compilers, but it is known to break if multiple inheritance is
used anywhere in the object hierarchy.

This patch introduces the cxx_header attribute to Python SimObject
definitions, which should be used to specify a header to include in
the SWIG interface. The header should include the declaration of the
wrapped object. We currently don't enforce header the use of the
header attribute, but a warning will be generated for objects that do
not use it.

tlb: Don't separate the TLB classes into an instruction TLB and a data TLB

TLB: Make all tlbs derive from a common base class in both python and C++.

SimObjects: Clean up handling of C++ namespaces.
Make them easier to express by only having the cxx_type parameter which
has the full namespace name, and drop the cxx_namespace thing.
Add support for multiple levels of namespace.

Fix various SWIG warnings

go back and fix up MIPS copyright headers

fix MIPS headers

Get MIPS_SE actually working again by actually by fixing TLB stuff and running hello world

Add in files from merge-bare-iron, get them compiling in FS and SE mode

Address Translation: Make SE mode use an actual TLB/MMU for translation like FS.