dmaengine: idxd: set DMA_INTERRUPT cap bit

Even though idxd driver has always supported interrupt, it never actually
set the DMA_INTERRUPT cap bit. Rectify this mistake so the interrupt
capability is advertised.

Reported-by: Ben Walker <benjamin.walker@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/164971497859.2201379.17925303210723708961.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>