scripts: logging: support native_posix dictionary logging

- Do not look CONFIG_* symbols from dynamic symbols which might
  be there before the symbol table where CONFIG_* symbols are found.

- Define posix architecture in ARCHS list.

- Check if architecture is not found instead of letting the code
  run into trying to access dictionary with None key.

Signed-off-by: Miika Karanki <miika.karanki@vaisala.com>