dmaengine: idxd: add capability check for 'block on fault' attribute

The device general capability has a bit that indicate whether 'block on
fault' is supported. Add check to wq sysfs knob to check if cap exists
before allowing user to toggle.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/162802992615.3084999.12539468940404102898.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>