systemc: Add the deprecated sc_module::end_module function.

The regression tests use this function. In the Accellera implementation
it seems to just do some error checking, so our version doesn't do
anything for now.

Change-Id: Icaad45e934bad69e301bc0234f73e69791940736
Reviewed-on: https://gem5-review.googlesource.com/10854
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>