systemc: Distinguish internal events from normal sc_events.

The internal events aren't supposed to show up in the namespace or as
children of objects.

Change-Id: Id04b9bfe2e1f8f216390dd989797558eaf33d715
Reviewed-on: https://gem5-review.googlesource.com/c/13309
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

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: Implement sc_event_queue.

Change-Id: I58fd72b8c64ee82eb478d810f7114bab7a31cbfa
Reviewed-on: https://gem5-review.googlesource.com/c/13184
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Define the nonstandard sc_event_queue_port typedef.

Used in the tests.

Change-Id: Ic4b4a313b2bd02e5cb3ec07c4f7ee79219728881
Reviewed-on: https://gem5-review.googlesource.com/11262
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>