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: CONFIG_L1_CACHE_LINE_SIZE_BITS in cmake

Move definition of L1_CACHE_LINE_SIZE_BITS to cmake where it is set
according to the arm processor family.

This removes duplication in the hardware.h header files and makes adding
a new processor family require less lines changed.

ARM/SMP: define IPI_MEM_BARRIER for ARM, that's used in generic smp/ipi.c

aarch64: Initial implementation

arm: Remove duplicate definitions

PPTR_TOP and KS_LOG_PPTR are defined in the mode headers, this commit
removes the duplicate definitions in the general arm header

Benchmark: share and use KS_LOG_PPTR and PPTR_TOP for x86 and ARM

Rearranging headers for aarch32 to 32/mode/*

unsigned int -> word_t

Rename uint32_t -> word_t in any relevant places

Recommit of arm_hyp branch on release snapshot

Release snapshot