dmaengine: ioatdma: Set non RAID channels to be private capable

This allows claiming of non-RAID channels as a private channel. This
prevents breakage of MDRAID using the IOATDMA channels via
async_tx but also allows agents such as NTB to claim channels
exclusively for its usages.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>