systemc: Use the stage of simulation and not port size in add_trace.

The assumption was that a port wouldn't have any interfaces until
after elaboration, and that if it would be traced, it would have
interfaces. Checking if the simulation has started (and hence
elaboration has finished) is a more accurate and direct way to check
the same thing.

Change-Id: I7fe9ecea469997d1a257dd3e4a0db31889aff722
Reviewed-on: https://gem5-review.googlesource.com/c/13195
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

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>

systemc: Implement most of sc_inout.

Because sc_inout needs sc_dt::sc_logic and that probably calls
functions from dt_sc_mempool.cc and because those hadn't yet been
stubbed out. This change adds stubs for those as well.

Change-Id: I544a1669575b594d4612558b8b6f47668ac94414
Reviewed-on: https://gem5-review.googlesource.com/12221
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Add in the deprecated binding port constructors.

These are needed by... you guessed it, the regression tests.

Change-Id: Id30e71944cc7f3faca7dcb197f37938368364fcd
Reviewed-on: https://gem5-review.googlesource.com/10958
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Stub out the predefined channels.

Change-Id: Ie030aad26875bd49e54981ec1e9076b7b5af6630
Reviewed-on: https://gem5-review.googlesource.com/10839
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>