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.

style: consistently attach return type

Add attach-return-type to astyle

x86: Manually declare array of chars instead of using string literals

This is to work around the problem of the C parser not being able to parse string literals

x86: Add BSS regions for BOOT and PHYS code

Uninitialized data structures in BOOT and PHYS code currently get
placed in sections that are allocated in the file of the final image.
Whilst these sections will get reclaimed during kernel boot, so no
runtime memory is being wasted, it results in kernel images that
are much larger to load and transport than necesary.

This change adds explicit BSS regions for both BOOT and PHYS code
and moves all appropriate data structures into them

x86: Fix cpuid family/model composition

Fixes a bug where previously MODEL_ID() was defined as:
`#define MODEL_ID(x) ( ((x & 0xf0000) >> 16) + (x & 0xf0) )`

This was incorrect because (1) it didn't take into account the conditional
nature of the extended_model_ID, and (2) it's actually shifting the
extended_model_ID into the low bits and keeping the model_ID in the high bits,
when it should be the other way around.

This patch also introduces a foundation for more sane testing of CPU vendor,
family, model and brand_ID.