systemc: Add in the deprecated binding port constructors.

These are needed by... you guessed it, the regression tests.

Change-Id: Id30e71944cc7f3faca7dcb197f37938368364fcd
Reviewed-on: https://gem5-review.googlesource.com/10958
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>