Minor restructuring of Python config code, mostly to avoid walking

Minor restructuring of Python config code, mostly to avoid walking
the source tree for *.odesc files every time we run the script.
This is now factored out into load_odesc.py, which should be used
to generate m5odescs.py, which is then used as the source of object
& parameter definitions.

util/config/m5configbase.py:
    - Move odesc loading code to separate load_odescs.py, so maybe someday
    that can be done once at build time.
    - Print out children of a node in the order they are added.
    - Automatically assign a parent-less node to the first node for which it
    is used as the value of a parameter.  (Easier demonstrated than explained.)
    - Calculate object paths dynamically when requested rather than trying
    to keep them up to date as objects get assigned to parents.

--HG--
rename : util/config/m5config.py => util/config/m5configbase.py
extra : convert_revision : 2183a09d32f3862ab377e0a929715f30505a03cb