systemc: Add a stubbed out sc_object class.

Also add a SConsopt variable USE_SYSTEMC to hide systemc support until
it's usable.

Change-Id: Ibb37483432b147ee690a36bb5c8dd74f1c4c7ae4
Reviewed-on: https://gem5-review.googlesource.com/10821
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>
5 files changed