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.

Add stdint MAX definitions

- UINTPTR_MAX
- UINT64_MAX
- UINT32_MAX
- INT64_MAX
- INT32_MAX

conversion: fixed unnecessary word_t change

Change additional int->word_t due to interraction with the C parser to ease verification

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

generate warnings for incorrect format strings for kprintf, bring stdint.h
inline for x86 and arm and fix some format strings as a consequence

Release snapshot