replacing all ifndef with pargma once

All the kernel header files now use pargma once rather than the ifndef,
as the pre-processed C files do not change while header files
are protected with pargma once. This will also solve any naming issues
caused by ifndef.

Convert license tags to SPDX identifiers

This commit also converts our own copyright headers to directly use
SPDX, but leaves all other copyright header intact, only adding the
SPDX ident. As far as possible this commit also merges multiple
Data61 copyright statements/headers into one for consistency.

style: consistently attach return type

Add attach-return-type to astyle

Refactor logic for cap revocability in cteInsert into new function with arch case

Revocability of a cap, with respect to its parent, is a general property on caps and
makes sense to be abstracted. This allows for the addition of an arch case without
further complicating the cteInsert function itself.

arm: Use #define for tcbArchCNodeEntries

Using a #define allows the post processed C code to be identical
for the purposes of verification

SELFOUR-287: 32-bit vt-x implementation

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

Rearranging headers for aarch32 to 32/mode/*

unsigned int -> word_t

Rename uint32_t -> word_t in any relevant places

ARM: Replace various direct use of __attribute__ with util.h abstractions.

Use of these abstractions aids compiler portability, as only a single place in
the kernel needs to be adapted. This commit is not intended to affect either
verification or generated code.

Move object size definitions to arch specific headers

The size of these objects cannot be considered a common constant as
they will be different in the upcoming 64-bit ports

refactor tcb_t to remove duplication between x86 and arm header files

Update the size of tcb structure.

add compile asserts to check objects are the sizes we expect them to be

Introduce 'Notification Binding': a new feature which allows a tcb to be bound to a single asynchronous endpoint.

Refactor some common elements across arm and x86 structures.h files.
This change purely changes the ordering of C symbols, as well as
adding some extra checking

Add ability to set a human readable thread name when running kernel in debug mode

trivial: style

further support for XN bit on ARM

Recommit of arm_hyp branch on release snapshot

Release snapshot