Make kernel log buffer derived from cmake config

This removes the explicit CMake configuration for the kernel log buffer
and replaces it with a #define that is enabled for the required
configurations.

Signed-off-by: Curtis Millar <curtis@curtism.me>

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.

SELFOUR-518: User-level log buffer

Remove global ksLog and use KS_LOG_PPTR instead

Benchmark - Log buffer: use global page table

Release snapshot