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>