[reggen] Error check for data-intg-passthrough

The reggen supports an option called `data-intg-passthrough` on windowed regions.
If this variable is true, it basically means beyond the window region there is already data integrity, thus the data integrity should not be generated for it in reg_top (the integrity for registers will instead be moved to `tlul_adapter_reg`).

Having said that, the current scripting does not really handle / check the case if a reg block has multiple windows each with different expectations on `data-intg-passthrough`. We do not have this case right now, but it would be good to explicitly add an error check to ensure all windows either agree or disagree.