[arch][mmu] add more test code to the mmu routines
[arch][mmu] add more test code to the mmu routines

Create a user space address space, map some pages, query the pages,
context switch, to the new aspace, access the pages.

Basic test that the aspace abstraction is working.

Will generate errors on some of the arches that dont fully implement all
of this, but not a crash.

hollanderic/lkstuff,hollanderic/lkstuff,littlekernel/lk,hollanderic/lkstuff,hollanderic/lkstuff,littlekernel/lk,littlekernel/lk,littlekernel/lk