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

Abstractly declare a threads registers have changed

This removes an #ifdef for x86-64 that was in generic code by declaring the generic
mechanism that is being used as an Arch_ function

Change hasVCPU to generic archInfo boolean in public interfaces

The Arch_hasVCPU function instead of cheaking for whether a thread has a VCPU was
specifically checking for whether a thread on aarch32 had a VCPU, as that was the
condition needed to be passed into sanitiseRegister. This made the implementation
on x86 extremely confusing as Arch_hasVCPU was implemented to return false due to
there being no need for sanitiseRegister on x86 to know whether there was a vcpu.

This commit changes hasVCPU variables to be an abstract archInfo boolean that can
be used arbitrarily by an architecture. Arch_hasVCPU function was also changed to
become Arch_getSanitiseRegisterInfo whose result only passed to sanitiseRegister.

Refactor sanitiseRegister to take a bool rather than a (tcb_t *).

This involves adding a function to determine if a tcb has a vcpu, and
makes verification a lot easier for arm-hyp.

Pass tcb_t to sanitiseRegister instead of arch_tcb_t

Remove incorrect CONST usage

This removes usages of CONST Arch_activateIdleThread. According to
gcc 'a function that has pointer arguments and examines the data
pointed to must not be declared const'. Whilst these functions do
not presently examine their tcb_t pointer argument, it seems
pointless to pass something that can never be safely looked at.

Further a function that returns void and is CONST is utterly meaningless

x86: Make x86 the name of the architecture instead of IA32

IA32 is 32bit version of the x86 architecture. Whilst only IA32
is supported, much of the code is generic x86. Using a generic
x86 architecture will aid in future 64bit support