systemc: Centralize how object parents are chosen.

There's a lot of repeated code for this. Also, the sc_vector type
needs to be able to artificially inject a parent for the objects it
creates.

Change-Id: I76f9b551632cd2cd70e26741b215290b35c382e9
Reviewed-on: https://gem5-review.googlesource.com/c/13194
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Report a warning if an event or object needs to be renamed.

Change-Id: I8085ba19fd7acd69d07a1e032f2fd18b6c5fed6f
Reviewed-on: https://gem5-review.googlesource.com/c/12598
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Ensure all objects and events have unique names.

Change-Id: I59b78048849953773b80bb2dac9b834762625331
Reviewed-on: https://gem5-review.googlesource.com/c/12439
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Fix a couple memory errors.

Because events are held in vectors, it doesn't make sense to keep an
iterator into the parent to keep track of where that event is for easy
removal since the iterator becomes invalid when the vector is changed.

The events need to be stored in a vector because systemc defines an
accessor which returns that vector, and building a vector on the fly
would be cumbersome.

Also, make sure the Event parent pointer is set to nullptr if there
isn't a parent.

Change-Id: I63a676190e7747e60baaca50009161d47bfc1c54
Reviewed-on: https://gem5-review.googlesource.com/12039
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Make orphans top level objects instead of panic-ing.

When a simulation ends, the sc_objects it contains are destroyed one
by one, not necessarily in hierarchy order. That means that a parent
object can legitimately be destroyed before its children. Instead of
panic-ing when that inevitably happens, this change makes gem5 turn
those children into top level objects.

Change-Id: Icad9c99310fbc3ddcadbbb4f8a990b4fbfe35bdf
Reviewed-on: https://gem5-review.googlesource.com/12035
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Implement much of events, event lists and event exprs.

Three things aren't yet implemented, waking up processes which are
sensitive to the event, triggering of events, and garbage collecting
list objects which came from expression objects.

The garbage collection aspect is problematic since there doesn't seem
to be a correct way to implement it given the constraints in the spec,
including the way that's implemented by Accellera. It's something that
will need to be dealt with at some point, but in the interest of
forward progress it's being ignored for now.

Change-Id: Ic4e3c219ff482729f1f1302ab10181a798d48041
Reviewed-on: https://gem5-review.googlesource.com/11711
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Implement most of sc_object.

To avoid making it hard to change sc_object's implementation in the
future, this change keeps most of the data members out of sc_object and
keeps them in a seperate Object which is managed independently but
still matches to the sc_objects one to one.

This change also moves away from the SystemC/sc_gem5 namespace pair in
favor of sc_gem5. Having two namespaces with classes, etc, living in
both was complicating things. Having to use a namespace that doesn't
fit in one scheme or the other isn't great, but it's the lesser of two
evils.

Change-Id: Ib59c3c515ca98c7fe519c59e9fe9270304b71cc0
Reviewed-on: https://gem5-review.googlesource.com/11611
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>