Make python style compliant

Brings the python files in this repo into compliance with the
checks in `sel4_tools`.

Convert to SPDX license tags

This includes marking all documentation files CC-BY-SA-4.0.

python3: Fix compatibility issues between versions

Small fixes that allow running scripts with python3.

untyped_gen: remove code for dealing with rootserver

We now expect the elfloader and kernel boot to place the rootserver at
the end of available memory. This means that we can ignore them when
allocating from the start of memory (as long as they do not conflict
somewhere in the middle).

untyped_gen: round regions to page boundaries

This is to match the current behaviour of the elfloader.

cdl_utils: get untyped_gen to run

cdl_utils: add untyped gen

This replicates kernel untyped creation and can be called from the build
system to get a list of untyped