make it so that pio devices must respond with some delay.
dev/io_device.cc:
don't forget to include dma_interface.hh so we could use it.
dev/io_device.hh:
the generic BusInterface isn't enough for doing DMA
we need the actual DMAInterface
--HG--
extra : convert_revision : 70298d33c8520a3f4ad11aa600825a8cec7e44bf