systemc: If no sc_module_name was used, throw an error.

systemc: If no sc_module_name was used, throw an error.

This is tested by the regression tests. Also make sure the handshake
which sets up instances of sc_module is cleaned up if we bail partway
through for some reason, for instance if an intermediate class throws
an exception as part of its constructor.

Change-Id: I89afe5f76832cc132aa2bb8f19916dea64546784
Reviewed-on: https://gem5-review.googlesource.com/12251
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>