systemc: Get rid of leftovers from unimplemented warnings past.

These warnings were removed when the functionality they warned about
was implemented, but there were some leftovers like unnecessary
includes and some helper functions which hid gem5 specific headers
from the ext directory.

Change-Id: Ic886ac0f1264687524e3a7b7eaab8836f318a5a2
Reviewed-on: https://gem5-review.googlesource.com/c/13398
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Switch to using predefined messages for utils.

Create and use predefined messages for utils which match the ones
Accellera uses.

Change-Id: I932b7206fc16181d01a0d5b7441ce617b30e5365
Reviewed-on: https://gem5-review.googlesource.com/c/13328
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Refactor reporting to prep for int based messages.

There's a deprecated reporting mechanism based on integer message ids,
and the reporting mechanism needs to be refactored a bit to make it
easier to support.

Some bookkeeping data structures were moved out to somewhere they
can be accessed by other code, obviating the non-standard get_handler
function.

Change-Id: Id427cd79be9ef0f3275fbac39ff047ab672fb3e0
Reviewed-on: https://gem5-review.googlesource.com/c/13318
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: Stub out all the standard utilility classes and functions.

Change-Id: I9e9724edb6281e0b0a6bae5546b0ede77d295c12
Reviewed-on: https://gem5-review.googlesource.com/10841
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>