dmaengine: idxd: device cmd should use dedicated lock

Create a dedicated lock for device command operations. Put the device
command operation under finer grained locking instead of using the
idxd->dev_lock.

Suggested-by: Sanjay Kumar <sanjay.k.kumar@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/161894525685.3210132.16160045731436382560.stgit@djiang5-desk3.ch.intel.com


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