Relax assertion in Debug.scala, allow dmactive to be used to exit from busy state in DM (#1782)

src/main/scala/devices/debug/Debug.scala

@@ -1181,7 +1181,7 @@ class TLDebugModuleInner(device: Device, getNComponents: () => Int, beatBytes: I
     }.otherwise {
       ctrlStateReg := ctrlStateNxt
     }
-    assert ((!hartExceptionWrEn || ctrlStateReg === CtrlState(Exec)),
+    assert ((!io.dmactive || !hartExceptionWrEn || ctrlStateReg === CtrlState(Exec)),
       "Unexpected EXCEPTION write: should only get it in Debug Module EXEC state")
   }
 }