dma_xfer_req

I added an encoder in between the TX DMA and the DAC FIFO, and all the AXI signals go in and out of the encoder, but there's this one signal left called dma_xfer_req. It's produced by the DMA and consumed by the FIFO, but I have not yet figured out how to handle it. I think I'm going to have to have the encoder detect it and pass it along so that the FIFO works correctly. For now, while I'm trying to deal with some other errors, I've left it in place. You can see it in the cover image.