memtest: Memtester support for DMA

This patch adds DMA testing to the Memtester and is inherits many changes from
Polina's old tester_dma_extension patch.  Since Ruby does not work in atomic
mode, the atomic mode options are removed.

configs/ruby/MI_example.py

@@ -132,6 +132,10 @@ def create_system(options, system, piobus, dma_devices):
                                    dma_sequencer = dma_seq)
 
         exec("system.dma_cntrl%d = dma_cntrl" % i)
+        if dma_device.type == 'MemTest':
+            system.dma_cntrl.dma_sequencer.port = dma_device.test
+        else:
+            system.dma_cntrl.dma_sequencer.port = dma_device.dma
         dma_cntrl.dma_sequencer.port = dma_device.dma
         dma_cntrl_nodes.append(dma_cntrl)