systemc: Don't use write() in sc_clock to set the clock value.

The two different processes we have to use to match Accellera behavior
would trip the checks in write.

Change-Id: Iee729b239bccd8f7b854894000c9ef2c47600563
Reviewed-on: https://gem5-review.googlesource.com/c/13202
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Implement a significant portion of sc_clock.

Change-Id: Ic195f46ac13b46a02c86a5fc8d90ba66a415a9c8
Reviewed-on: https://gem5-review.googlesource.com/12215
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

systemc: Add the nonstandard time_stamp function.

Change-Id: I608c390b125611e5b62483c7e8567bb5479df553
Reviewed-on: https://gem5-review.googlesource.com/11281
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>

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>

systemc: Stub out the predefined channels.

Change-Id: Ie030aad26875bd49e54981ec1e9076b7b5af6630
Reviewed-on: https://gem5-review.googlesource.com/10839
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>