dmaengine: idxd: set DMA channel to be private

Add DMA_PRIVATE attribute flag to idxd DMA channels. The dedicated WQs are
expected to be used by a single client and not shared. While doing NTB
testing this mistake was discovered, which prevented ntb_transport from
requesting DSA wqs as DMA channels via dma_request_channel().

Reported-by: Srinijia Kambham <srinija.kambham@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Tested-by: Srinijia Kambham <srinija.kambham@intel.com>
Fixes: 8f47d1a5 ("dmaengine: idxd: connect idxd to dmaengine subsystem")
Link: https://lore.kernel.org/r/161074758743.2184057.3388557138816350980.stgit@djiang5-desk3.ch.intel.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>