systemc: Ensure the reset event is notified before reseting the target.

systemc: Ensure the reset event is notified before reseting the target.

The target may be the process which is currently running. In that case,
the reset method will end and never get to notifying the reset event.
To fix that, we need to notify the reset event first.

Change-Id: If3a9d87edc0999293a68d86d35989ae49eab3c07
Reviewed-on: https://gem5-review.googlesource.com/c/13187
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>