ruby: fix MOESI_hammer directory to work with > 3GB memory

ruby: fix MOESI_hammer directory to work with > 3GB memory

The MOESI_hammer directory assumes a contiguous address space, but X86
has an IO gap from 3-4GB. This patch allows the directory to work with
more than 3GB of memory on X86.

Assumptions: the physical address space (range of possible physical
addresses) is 0-XGB when X <= 3GB, and 0-(X+1)GB when X > 3GB. If there
is no IO gap this patch should still work.

Change-Id: I5453a09e953643cada2c096a91d339a3676f55ee
Reviewed-on: https://gem5-review.googlesource.com/2169
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>