config: Revamp memtest to allow testers on any level

config: Revamp memtest to allow testers on any level

This patch revamps the memtest example script and allows for the
insertion of testers at any level in the cache hierarchy. Previously
all created topologies placed testers only at the very top, and the
tree was thus entirely symmetric. With the changes made, it is possible
to not only place testers at the leaf caches (L1), but also to connect
testers at the L2, L3 etc.

As part of the changes the object hierarchy is also simplified to
ensure that the visual representation from the DOT printing looks
sensible. Using SubSystems to group the objects is one of the key
features.