stdlib,configs: Add DRAMSys to the gem5 standard library

Add DRAMSys as a new AbstractMemorySystem to the gem5 stdlib.
Also, provide convenient subclasses with predefined DRAMSys
configurations.

Add two new stdlib examples:
    - dramsys-traffic.py: Demonstrates the usage of DRAMSys
      using the stdlib TrafficGenerators
    - arm-hello-dramsys.py: A variant of the arm-hello.py
      script that uses DRAMSys as it's memory.

These DRAMSys memory components are only compiled into the standard
library if DRAMSys is not compiled into gem5.

Change-Id: I9db87c41fbd9c28bc44e9d6bde13fc225dc16be9
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/62914
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
6 files changed