systemc: Make TLM port wrappers for tlm_base_(target|initiator)_socket.

systemc: Make TLM port wrappers for tlm_base_(target|initiator)_socket.

These are useful if using TLM sockets without using the standard TLM
protocol. For instance, when used with ARM's fast models, this can wrap
sockets which carry the opaque GICv3Comms protocol.

Change-Id: I329a919068f958abbde2cb83683d3a3ae2e05a20
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20860
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>