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: clean & consolidate pmu management code

- consolidate armv_init_ccnt into arm_init_ccnt, which is general
- move armv_handleOverflowIRQ definition to benchmark.h
(no need for extra header)
- clean up definition of armv_handleOverflowIRQ

trivial: add missing config include

arm: consolidate benchmark_arch_utilisation_reset

- Move identical definitions from armv6 and armv7 to common arm code.
- Remove excessive #ifdef guards - let the compiler throw it away if
it isn't used

Fix armv6 CCNT definition

Provide a general ARM timestamp function

Use SYSTEM_READ_WORD, each platform defines the CCNT constant.

SELFOUR-448 Benchmark: Track thread's CPU utilisation time

SELFOUR-448: Benchmark: implement ccnt on armv6

SELFOUR-446 Unify code base for trace points and track feature

SELFOUR-446 Benchmark: Track syscall feature

Benchmark feature that currently:
- Keeps track of system calls info
- Start time
- Duration
- Capability type
- Invocation tag
- Log the number of invocations of each system call*
- Log the number of invocations for each capability type per syscall.
- Has 3 new syscalls (dump, reset, get size).
- This new feature uses the existing log buffer (which is 1MiB for x86
and ARM). Since the number of syscall invocations is not
deterministic, the logged number of invocations is limited by the size
of the buffer. I suggested to enable the users to pass their own
user-level buffer, to enable more flexibility, later.
- ENABLE_BENCHMARKS is now a parent config option of trace points and
system call track features, they can't be used at the same time.

Removed CONFIG_BENCHMARK config option. All checks for '#ifdef CONFIG_BENCHMARK' replaced with '#if CONFIG_MAX_NUM_TRACE_POINTS > 0'.

Release snapshot