systemc: Implement general and VCD trace support.

This doesn't include WIF trace support, but does make allowances for
adding it in the future.

Change-Id: Ifb62f40a7d8a13e94463930a44ac4b1cf41e3009
Reviewed-on: https://gem5-review.googlesource.com/c/12826
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

src/systemc/utils/SConscript

@@ -33,4 +33,6 @@ if env['USE_SYSTEMC']:
     Source('sc_report_handler.cc')
     Source('sc_trace_file.cc')
     Source('sc_vector.cc')
+    Source('tracefile.cc')
+    Source('vcd.cc')
     Source('warn_unimpl.cc')