cpu: Allow creation of traffic gen from generic SimObjects

This patch allows to instantiate a Traffic generator starting from a
generic SimObject, so that linking to a BaseTrafficGen only is no longer
mandatory. This permits SimObjects different than a BaseTrafficGen to
instantiate generators and to manually specify the MasterID they
will be using when generating memory requests.

Change-Id: Ic286cfa49fd9c9707e6f12a4ea19993dd3006b2b
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/11789
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

cpu: Unify error handling for address generators

Unify error handling and create factory methods for address
generators.

Change-Id: Ic3ab705e1bb58affd498a7db176536ebc721b904
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/11516
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

cpu-tester: Added ExitGen to TrafficGen

Added the ExitGen to the TrafficGenerator which allows an EXIT
state to be added to the TrafficGen configuration file. Entering this
state will cause the simulation to exit immediately. Please note that
if multiple TrafficGen instances have an EXIT state, the first of these
to be encountered will cause the simulation to terminate.

Change-Id: Ieea51f05ffb780771f007787a2b119f79143d0c1
Reviewed-by: Sascha Bischoff <sascha.bischoff@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/5723
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>