scripts: Convert gen_offset_header to Python

By having this as a Python script rather than a host executable, this
should simplify the build process on non-Unix platforms.

With this change, pyelftools is now required to build Zephyr.  Please
consult the getting started documentation for your host platform for
installation instructions.

Jira: ZEP-2062

Signed-off-by: Leandro Pereira <leandro.pereira@intel.com>
8 files changed