gpdma: make wakers accessible from DmaChannelImpl

# Conflicts:
#	src/gpdma/ch.rs

Author: astapleton

src/gpdma/future.rs

@@ -25,6 +25,7 @@ impl<'a, CH: DmaChannel> IntoFuture for DmaTransfer<'a, CH> {
     type IntoFuture = DmaTransferFuture<'a, CH>;
 
     fn into_future(self) -> DmaTransferFuture<'a, CH> {
+        self.enable_interrupts();
         DmaTransferFuture { transfer: self }
     }
 }