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: Refactoring traffic generators into separate files.

Change-Id: I2372a0a88e276dcb0c06c3d0a789e010cfba8013
Reviewed-by: Matteo Andreozzi <matteo.andreozzi@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/5722
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>