systemc: Implement port binding except positional binding.

systemc: Implement port binding except positional binding.

This change adds code which keeps track of ports and interfaces which
are being bound to be finalized later, and the actual port binding of
interfaces and recursive binding port ports.

Change-Id: Ifa885ed44b667254762cc101580be4f0a7d7a131
Reviewed-on: https://gem5-review.googlesource.com/12084
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>