Trim the arch mmu unit tests accordingly.
Should probably switch this to a #define, but it's possible some of
these queries could be dynamically detected (XN for example). May
revisit at some point.
Allow asking the arch layer if it supports NX pages or NS pages.
Have the arch mmu test code test accordingly.
Also tweak the tests to pass on arm32 mmu, which does not precisely
match the return semantics of the rest of the mmu routines on map/unmap.
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.
