Make `setvar region_paddr` works on x86-64

[dreamliner787-9]

Currently it does not work as the physical addresses of memory regions without a phys_addr attribute are determined at runtime in the capDL initialiser by the objects allocation algorithm.

To make this work we would need to make 2 changes to the initialiser:

1. Add a way to express "patch physical address of object A to virtual address B in VSpace C" in the capDL Spec.
2. Add a way to tell the allocation algorithm to allocate certain ranges of objects contiguously in physical memory. This is important because it would be reasonable for the user to expect their memory regions to be contiguous if they care about physical addresses.