Convert license tags to SPDX

Also clarifies provenance of code in `apps/fdtgen/fdt_utils.c`

Signed-off-by: Gerwin Klein <gerwin.klein@data61.csiro.au>

cakeml_regex: update to a more recent CakeML version

Since this was originally written, the syntax of theorem statements
changed, a conversion that breaks the proofs was added to the
default simpset, and and some of the functionality inlined here
was upstreamed to HOL4 libraries.

This is intended to run on CakeML version 6f71ec748.

Signed-off-by: Johannes Åman Pohjola <johannes.amanpohjola@data61.csiro.au>

cakeml_regex: update filterProgScript to account for HOL changes

cakeml_regex: Move filter_regex to .camkes file

Now that string attributes are supported on CakeML components we can
declare the regex as an attribute on the CakeMLFilter component and set
it in the ADL.

cakeml_regex: create application