systemc: Don't include the scheduler in an external header file.

The scheduler is an internal detail and shouldn't be exposed to the
headers in ext. It would transitively include more headers which are
not in ext, making it not self contained.

Change-Id: I8384cde9d19363953ffd0c91e7d8d27f8f79a570
Reviewed-on: https://gem5-review.googlesource.com/c/13336
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Implement register_port in all the predefined channels.

Something the Accellera implementation does which would be good to do
in the gem5 implementation is to create a base class for sc_signal
which isn't templated, and which holds the common/non-type specific
versions of the various sc_signal methods. This will reduce code
redundancy and binary size, and also let us hide more code in .cc
files so that it's less likely we'd need to recompile model code to
fix a bug.

Also, since this all uses of sc_channel_warn_unimple have now been
eliminated, remove that function.

Change-Id: Ia574647c034e7136093c2047b69de725ac34f52f
Reviewed-on: https://gem5-review.googlesource.com/c/13200
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Implement the sc_signal_rv channel and ports.

Change-Id: Id1a3fd2ded224bbe94a4a65e0acf34a3547aedcc
Reviewed-on: https://gem5-review.googlesource.com/c/12813
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>