stream: Remove app argument hack

The uint32_t *app argument doesn't exist in real hardware. It was a hack in
xilinx_axidma/enet to fake the (secondary) control stream connection. Removed
the argument and added the second stream to axienet/dma.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>
