clang: Fix errors on zero kernel devices

"const TYPE *ptr" creates a non-const pointer to const data; for the
pointer itself to be rodata requires "TYPE *const ptr".

Taking the size of the pointer is caught by -Werror by default; suppress
that.

Signed-off-by: Stefan O'Rear <sorear@fastmail.com>

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.

rename KDEV_PPTR/PPTR_KDEV to KDEV_BASE

This is the virtual address for the start of the kernel device mapping
region.

Create device untypeds at boot for all arches

Currently on x86 device untypeds are generated by passing the entire
address space minus any parts that are reserved by the kernel or that
are "real" memory (e.g. kernel image, physical RAM).

On ARM and RISC-V, device untypeds were generated at compile-time from
a device tree. This patch moves ARM and RISC-V to use the same approach
as x86, and moves the code from x86 into a common location that's
shared between the three architectures.

Co-Authored-By: Anna Lyons <anna@gh.st>

tools: rewrite hardware_gen.py

This is almost a complete rewrite from the old hardware_gen.py.

It separates the 'parse DT' stage from the 'generate output'
devices more strictly, and is hopefully easier to understand and
easier to extend.

We also no longer generate the 'devices' list (in YAML)
or the dev_p_regs array (in C), as the kernel will implicitly
expose all non-RAM untypeds as devices.