systemc: Expose the utility functions for payload->packet conversion.

These can be used anywhere someone needs to turn a packet into a
payload or vice-versa.

Change-Id: I26a1f134e6fbec81b230a2853cf79264e80bf2dc
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20859
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

systemc: Use the new TLM socket types in the TLM bridge SimObjects.

These are in the definition of the python version of the SimObjects.

Change-Id: Iadb143158815df68cf32cc254ad19f755ab4e78a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18173
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Teach the TLM bridges how to use gem5's new backdoor mechanism.

This change teaches the TLM bridges to translate between TLM's DMI
mechanism and gem5's backdoor mechanism.

Change-Id: I942a6cce4fb87f10e8173f4ee49b6c7b0ffa7e4a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17591
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Templatize the gem5/TLM bridge SimObjects.

The C++ side is templated, and there are python versions for each
(currently two) width of bridge supported.

Change-Id: I4baa9f22d4c87629d45e9e1292eb66c65d25a655
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17234
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Delete extra code from src/systemc/tlm_bridge.

Much of the code in src/systemc/tlm_bridge has been absorbed into the
TLM/gem5 bridge SimObjects and is no longer needed and redundant with
the original version in util/.

Change-Id: I0fa7af67649987cf9f6fc5cd4783002dde2242ac
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17233
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Create unified gem5/TLM bridge SimObjects.

These objects expose a standard TLM initiator or target socket with
width 64, and a gem5 slave or master port. What goes in one type of
port comes out the other with the appropriate conversion applied.

Change-Id: I65e07f746d46d3db0197968b78fffc5ddaede9bf
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17232
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

tlm: Initial import of tlm/gem5 bridge code.

This is a slightly mangled version of the existing bridge code in
util/tlm/src/. The changes fix some small style issues, change to gem5
specific include paths, and removes the Gem5SimControl code. That code
coordinates gem5 with the external systemc kernel, and in this usage
there's no external kernel.

The code imported here compiles, but it isn't yet expected to work.

Change-Id: I9c593a52e2554534720d21cd31a03e543ad897ad
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17231
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>