systemc: Track the module in the end_of_elaboration callback.

systemc: Track the module in the end_of_elaboration callback.

sc_objects constructed during that callback are considered children of
the module the callback belongs to.

Change-Id: I164863a10beef6d0e2c6d9c5e8f2642d80769dca
Reviewed-on: https://gem5-review.googlesource.com/12076
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>