mem: Record the request master ID in the PacketInfo structure.

That can be recorded in a packet trace.

Change-Id: I3813ab4ea5aadeb40b355ff01f10e8ecab2bb790
Reviewed-on: https://soc-sim-internal-review.googlesource.com/3482
Reviewed-by: Rahul Thakur <rjthakur@google.com>
Reviewed-on: https://gem5-review.googlesource.com/4780
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>

mem: Add Program Counter to MemTraceProbe

mem: Add PacketInfo to be used for packet probe points

This patch fixes a use-after-delete issue in the packet probe points
by adding a PacketInfo struct to retain the key fields before passing
the packet onwards. We want to probe the packet after it is
successfully sent, but by that time the fields may be modified, and
the packet may even be deleted.

Amazingly enough the issue has gone undetected for months, and only
recently popped up in our regressions.

mem: Add probe support to the CommMonitor

This changeset adds a standardized probe point type to monitor packets
in the memory system and adds two probe points to the CommMonitor
class. These probe points enable monitoring of successfully delivered
requests and successfully delivered responses.

Memory system probe listeners should use the BaseMemProbe base class
to provide a unified configuration interface and reuse listener
registration code. Unlike the ProbeListenerObject class, the
BaseMemProbe allows objects to be wired to multiple ProbeManager
instances as long as they use the same probe point name.