SELFOUR-114: remove bootinfo.h duplication

Change bootinfo to have generic slot region for paging structures

Current bootinfo defines two slot regions for paging structures,
one for page directories and one for page tables. This does not
easily generalise for N levels of paging structures. This change
uses a single region that has a known order of objects for however
many levels exist

unsigned int -> word_t

Rename uint32_t -> word_t in any relevant places

ia32: Large commit that implements PAE paging for x86

This commit involves the PAE paging itself, refactoring the
vspace code to extra what is common between PAE and 32bit paging,
as well as some renaming to not call the root paging structure
a PD

trivial: Standardise on 32-bit unsigned variables for domain values.

Domains are unnecessarily treated explicitly as 8-bit values within boot info.
Though there are existing proof constraints that limit the maximum domain value
to 8 bits, most of the code would permit domain values up to 32 bits. The
maximum value is unnecessarily constrained in boot info, a restriction which
this commit removes.

Closes VER-341

Release snapshot