Collapse some bits of repetitive code into their own procedures and

Collapse some bits of repetitive code into their own procedures and
allocate a maximally sized default object to back MAP_VPAGETABLE
mappings, allowing us to access logical memory beyond the size of the
original mmap() call by programming the page table to point at it.

This gives us an abstraction and capability similar to a real kernel's
ability to map e.g. 2GB of physical memory into its 1GB address space.