MLBEDSW-4417: Explicitly set packages in setup.py

This commit removes usage of the function
find_namespace_packages (which is not available in
older versions of setuptools) and instead explicitly
states the namespace packages in setup.py.

Signed-off-by: Dwight Lidman <dwight.lidman@arm.com>
Change-Id: I942f339953d50a7bf5fc3e83c0736813fea58dd2