Merge options cmake into general cmake file (#6989)

Merge options cmake into general cmake file (#6989)

This PR removes options/CMakeLists.txt and merges its contents into src/CMakeLists.txt and does some generalization in the mkoptions.py script. This prepares the whole setup so that we can also generate options code in other directories than options/ easily in the future: parts of the options code will be moved to the main folder.