dmaengine: idxd: add missing callback function to support DMA_INTERRUPT

dmaengine: idxd: add missing callback function to support DMA_INTERRUPT

When setting DMA_INTERRUPT capability, a callback function
dma->device_prep_dma_interrupt() is needed to support this capability.
Without setting the callback, dma_async_device_register() will fail dma
capability check.

Fixes: 4e5a4eb20393 ("dmaengine: idxd: set DMA_INTERRUPT cap bit")
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/165101232637.3951447.15765792791591763119.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>