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.

arm: Move SYSTEM_*_WORD macros to armv header file

This is needed to avoid circular include dependencies that result from
other header files trying to use these macros.

Move some lockTLB magic into C.

This patch moves the 'outer' chunk of lockTLBEntry into C rather
than handwritten assembly. The outer chunk accesses a global
counter and does arithmetic. The inner chunk (lockTLBEntryCritical)
writes to the registers, must be specially aligned, and is generally
special.

The change reduces unnecessary handwritten assembly, and also avoids
a special case that was problematic for binary verification.

ARM/v7-a: Force -O2 compilation of idle thread

This fixes a problem with -O0 SMP builds on ARM visible as kernel
data aborts whenever the idle thread executes.

The idle thread receives no stack pointer. At -O2, this is fine
as the wfi() call is inlined and stack operations in idle_thread
are optimized out. At -O0, the stack operations remain and wfi()
is not inlined, resulting in stack accesses in the idle thread
that cause data aborts.

Forcing -O2 behaviour was deemed the simplest solution for now.
Giving the idle thread a stack would have had larger verification
ramifications for what is now a fairly uncommon use case.

ARM: Add 32 bit directory for armv8-a

Remove many MODIFIES annotations.

These are redundant for any function which the C-to-Isabelle parser
actually analyses, which is now the vast majority of functions.

SELFOUR-614: calling halt() on the hikey platform results in infinite data abort
SELFOUR-408: halt does not halt

Remove assembly files for halt and idle thread and add wfi in armv.

Release snapshot