exporting DMA done signal to "outer world"

What I meant is if you put an intermediate component between the CPU and DMA that acts as an interrupt splitter then the DMA driver will no longer be associated to the interrupt. This is because the CPU will see the interrupt coming from the splitter and not the DMA. This intermediate component would act as a "hack-less" workaround to the problem. Also Qsys will make this much easier to do as there are various IRQ components at your disposal.

Your method to generate the DMA, re-import it into to make a static component, then hacking the HDL to export the IRQ signal will work as well. Then you would just have to associate the driver to the "new" component if you use the HAL driver. You might find it easier to just use the DMA driver macros since those just require you to pass in the DMA slave port address.