systemc: Add some deprecated features to sc_clock.*.

Add in two deprecated typedefs, and a deprecated constructor. These
are necessary to get the regressions to build.

Change-Id: Id8320a67c680acbca0abaee9898158ffd2678d67
Reviewed-on: https://gem5-review.googlesource.com/11183
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>