userError string written to IPC buffer

The format string in userError is now written to
the IPC buffer for debugging purposes.
This requires an snprintf which reuses vprintf with
a new structure for handling how output is done.

Signed-off-by: Saer Debel <saer.debel@data61.csiro.au>

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.

serial: remove putConsoleChar

putConsoleChar was needless indirection around putDebugChar. Remove
this.

Replace #pragma once with include guards

SELFOUR-624: fix ia32 debug build

- separate putDebugChar and putConsoleChar
- this only has effect on x86 where 2 serial ports are initialised by
the kernel
- for arm, putConsoleChar just calls putDebugChar

SELFOUR-624: remove redundancy in io.[c|h]

And clean up a bit while we are there

Further separate 'release' and 'verification' builds

Originally building the kernel was largely considered to be done in
one of two ways
1. Release build with no assertions, no debug symbols and no printing.
This was generally considered to be a 'verified' build
2. Debug build with assertions, debug symbols and printing

Since then various options were added, such as the 'code injection'
option, which we wanted on builds that did not have assertions or
other options that affected performance. As such it did not depend
upon a debug build and had large warning signs saying that enabling
this in a release build would not give you a verified or trusted
kernel.

Most recently the ability to print from the kernel in release mode
was added. For the same reason that tying the ability to print with
the performance reduction of various debugging was not always desireable.

This change attempts to unify the current state and have a single top
level option to enable a 'verification friendly' build. All other
options (assertions, printing, code injection) then depend upon
this configuration not being set.

unsigned int -> 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

xIntroduce RELEASE_PRINTF, which allows a renamed printf (release_printf) to be used in a release build of the kernel - userful for debugging tests that only fail on a release build of the kernel

Release snapshot