systemc: Update the sc_main.py config to use m5.systemc.

Change-Id: I386970b5cf7ee1262b259abfb3b5e902ccea9991
Reviewed-on: https://gem5-review.googlesource.com/c/16568
Maintainer: Gabe Black <gabeblack@google.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>

systemc: config: Don't inject a custom argv[0] in sc_main.py.

argv[0] is already part of sys.argv, so we don't need to add an
additional argument in front of sys.argv.

The argv[0] which is used in gem5 config scripts is the name of the
config script itself. While it might seem a little odd for the name of
a systemc program to end in .py, it's as arbitrary as any other name,
and generally shouldn't cause a problem. If some other more
sophisticated mechanism for setting argv[0] is necessary, then the user
can write a very slightly more complicated version of this script with
additional logic.

Change-Id: Ifd5d8a02d3cd5db76054151ed6c7a7b1f8495fa8
Reviewed-on: https://gem5-review.googlesource.com/c/16342
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>

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>