Handle the DMA TX in a similar way as we do for the RX: in the DMA
completion callback.

Since we are no longer using DMA completion interrupt for the TX we can as
wall keep these interrupts disabled, but keep the handler for debug
purposes.
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>