systemc: Remove some old warn includes from ext/channel.

The calls to sc_channel_warn_unimpl have been removed, so the includes
aren't needed.

Change-Id: I58a916a7c4ef9a266be591789696457799b6b8dd
Reviewed-on: https://gem5-review.googlesource.com/c/13198
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Make sc_out delegate to its base class sc_inout.

The spec says these are essentially identical classes, they just have
both so that users can show their intent.

Change-Id: I51908edca89acea25891a52bfa7fca0681ccfc5c
Reviewed-on: https://gem5-review.googlesource.com/12220
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>