The main python script composing a single HMC device as a sub-system and specifying

all its parameters. I would like to mention that, one can easily instantiate multiple instances of the HMCSystem

class and build a network of HMCs, but this patch instantiates only one.

This patch and the subsequent chain of patches aim to model a simple Hybrid Memory Cube device in gem5

Please apply the complete chain before running the simulation.