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.

Move timestamp_t definition to types.h

it was causing circular references in files where it is defined and
hardware macros are also used.

Remove assumption on 32-bit memory offsets

On 64-bit platforms physical address could be >2^32 offset from a virtual address. This
changes offsets to match the word size of the target architecture

Add missing seL4_Uint16 type in the kernel

This type is provided by libsel4 and should be provided by the kernel in the future event
that shared headers actually use the seL4_Uint16 type

x86: add logical id mapping for x2APIC IPI boradcasting

x64: Check size of unsigned long

SELFOUR-114: remove bootinfo.h duplication

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

SELFOUR-244: symlink duplicated files from libsel4 into kernel rather than duplicating them, remove sanity target as a result

Rationalize standard types

This commit aims to rationalize how we represent different types
for compatiblity between ARM and x86, as well as between 32 and
64 bit code. The choices being made here is to declare that a
uint32_t has a type of 'int', this allows uint32_t to be declared
consistently across 32 and 64 bit (at least in GCC).
The word_t type is declared using a 'long' (not a uint32_t or uint64_t) to
allow for a word_t to be backed by the same type on both 32 and 64 bit
All other types that want to be declared as the size of a native word
get declared in terms of a word_t

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