systems/cva6_desc: Various fixes

[iburaky-ids]

dma_desc_wrap.sv:

• idma_backend's axi_req* and axi_rsp* were changed to protocol_req* and protocol_rsp* in b9d7f04 , but the same changes were not made to dma_desc_wrap.sv, this is now fixed
• RepWidth and StrideWidth are undefined, and unless I missed something in the macros, reps_t and strides_t are not used, therefore those lines are now removed

dma_reg_to_axi.sv:

• Verilog does not require a backslash to break lines of code and I get an error in QuestaSim with the backslash

[thommythomaso]

Thank you for your contributions. Merged as part of PR #36. Closed.