configs: Add an example workloads module

configs: Add an example workloads module

This will be a collection of Workload types.
At the moment we provide the following:

* ArmBaremetal: modelling a simple baremetal workload
* ArmTrustedFirmware: modelling the arm trusted firmware workload

Change-Id: Ib46286c03a1c952f981b172c1ea6aa4a6668757e
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Ciro Santilli <ciro.santilli@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/27969
Tested-by: kokoro <noreply+kokoro@google.com>