Decide if we want to change the names of the PS/PL DMA access debugfs attributes

Currently the debugfs attributes use the names dma_ps/pl_ddr but they in fact allow performing DMA across the whole address space, not just DDR, so might want to remove the ddr from the file names.

It is important to consider also the zynqmp EDGE plugin, since it probably expects the dma_ps_ddr and dma_pl_ddr debugfs files and it will also need to be modified.

See also #32 (closed) for important context. In the end, we might simply provide one debugfs file that allows DMA over the whole address space (or, roll-back to a restricted DDR-only, in which case we will need to keep the two separate debugfs files).