python: Add importer to standalone gem5py_m5

I believe the point of this binary was to allow people to use the m5
objects without the entire gem5 binary. However, without adding the
importer call, this did not work. Unfortunately, with the importer call
there is a circular dependence on the original gem5py.cc file.
Therefore, this change creates a new file that has the importer call.

Now, with the `gem5py_m5` binary you can run python code that references
modules in `src/python`. Note that `_m5` is not available, so anything
that depends on the gem5 SimObjects' implementation will not work.
However, thic can still be useful for things like getting Resources,
processing stats, etc.

Change-Id: I5c0e5d1a669fe5ce491458df916f2049c81292eb
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>

src/SConscript

@@ -639,7 +639,7 @@ gem5py_env.Program(gem5py, 'python/gem5py.cc')[0]
 m5_module_source = \
         Source.all.with_all_tags(env, 'm5_module', 'gem5 lib')
 m5_module_static = list(map(lambda s: s.static(gem5py_env), m5_module_source))
-gem5py_env.Program(gem5py_m5, [ 'python/gem5py.cc' ] + m5_module_static)
+gem5py_env.Program(gem5py_m5, [ 'python/gem5py_m5.cc' ] + m5_module_static)
 
 
 # version tags