systemc: configs: Add a very simple config which just runs sc_main.

systemc: configs: Add a very simple config which just runs sc_main.

This config will just run the sc_main function (which must have been
provided in c++ somehow), passing through any of the scripts command
line arguments to sc_main.

Needing to do this sort of thing is common enough that there should be
a canned config which supports it.

Change-Id: I8f88ba4776b9ec919dd8145a58cd856e11ac4e77
Reviewed-on: https://gem5-review.googlesource.com/c/16287
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>