Safe iDMA instantiation: guard against parameters mismatches

[colluca]

When instantiating idma_backend_rw_axi care has to be taken to pass the same AR channel through parameters read_meta_channel_t and axi_req_t.

In particular, during iDMA integration in Occamy to replace the legacy system DMA, read_meta_channel_t was wrongly misconfigured to use the AR channel from the frontend configuration interface, and the ID width mismatch would lead to malformed AXI requests from the backend.

I don't understand the need for the two somewhat redundant parameters, but I can think of two solutions to make instantiating the iDMA less error-prone:

• provide wrappers which instantiate frontend, midend and backend, deriving "redundant" parameters internally
• add assertion checks within the backend or transport layers to verify that "redundant" parameters match

I think the first would be the most valuable approach, but the second might still be valuable for iDMA developers in the development phase.