x86: Consistently compare against PPTR_USER_TOP

PPTR_USER_TOP is the last valid user address and so any address greater than it
should not be used. Due to pages being at least 4K aligned it is also correct
to do a >= comparison, but it is clearer and more consistent with verification
to perform just >.

x86: Rationalize names of paging structures

Changes the name of paging structure entries to more clearly indicate the kind of object
they map to. Generally this is changing a `pde_small` to `pde_pt` to indicate that this
mapping refers to a page table, removing an inconsistency where `pde_large` indicated that
the mapping was for a large page. For the same reason the `ept_pde_4k` type is changed to
`ept_pde_pt` type to reflect what is present in the actual entry.

`pde_large` is left as 'large' and not explicitly given a size as code common between
ia32 and x86-64 manipulates these entities and 'large' is already a used abstraction
over the two potential page sizes so there is need to introduce a formal abstraction layer
and make the names in the structures more specific.

SELFOUR-1062: Hide all VT-x related code behind #ifdef guards

The VT-x implementation is not going to be verified at the moment, and so the code for
it needs to be hidden from verification, which we do by #ifdef'ing it out if the VT-x
is not enabled. As a result the VT-x configuration depends on a non verification target

Share linker.h between architectures

x86: Restructure performASIDPoolInvocation

Swap the `if` cases in this function so that the default else case becomes one that
always happens, with an `assert`, and the vtx case becomes guarded with a config_set
This ensures that
* All code paths have either a check or assertion on having a correct cap type
* Compiler can see that all code paths will correctly set `asid_map` before using it

[STYLE_FIX]

Avoid using bitfield generated *_ptr_new functions

These functions can cause slow down during verification C parsing and do not currently
have any proofs about them. More importantly there is no performance impact from just
calling the regular *_new functions instead

SELFOUR-879: expose index and entry constants

SELFOUR-501: x86 - Remove PAE support

x86: Add BSS regions for BOOT and PHYS code

Uninitialized data structures in BOOT and PHYS code currently get
placed in sections that are allocated in the file of the final image.
Whilst these sections will get reclaimed during kernel boot, so no
runtime memory is being wasted, it results in kernel images that
are much larger to load and transport than necesary.

This change adds explicit BSS regions for both BOOT and PHYS code
and moves all appropriate data structures into them

x86: use setMR instead of setRegister in vspace.

Otherwise if the number of MRs is altered this code can break.

SELFOUR-634: support for TLB and cache management

SELFOUR-287: 32-bit vt-x implementation

This is an implementation of vt-x for x86 kernels running in
ia32 mode.

SELFOUR-632: implement cores non-architecture dependent structres

SELFOUR-556: Rationalize BITS vs INDEX_BITS

s/PD_BITS/PD_INDEX_BITS
Current convention is to say that X_BITS is the log base 2
size of an object, not the log base 2 number of indices

SELFOUR-556: Rationalize BITS vs INDEX_BITS

s/PT_BITS/PT_INDEX_BITS
Current convention is to say that X_BITS is the log base 2
size of an object, not the log base 2 number of indices

SELFOUR-617: one source of memory object sizes

Adds the following constants to libsel4
and uses them in the kernel.

seL4_SectionSize (arm)
seL4_SuperSectionSize (arm)
seL4_HugePageSize (x86 - pae)
seL4_LargePageSize (arm)
seL4_DataFault
seL4_InstructionFault

trivial: style

SELFOUR-484 x86: Get status bits invocation

This adds an invocation on page directories that returns the
status (accessed + dirty) bits of mapping.

trivial: style

SELFOUR-449 Implement user stack trace on double fault

x86: Use typedef for vspace roots instead of void*

SELFOUR-114: remove duplication of seL4_MessageInfo_t, adjust naming to avoid cparser mangling

x86: Extract 32-bit specific vspace functions in mode/vspace.c

x86: With multi-kernel support removed make the kernel PDs etc global instead of passing them around

x86: Rename constants and functions to have X86 prefix instead of IA32 prefix

x86: Move 32-bit specific files into 'mode' directories, and only build if IA32