dmaengine: idxd: add sysfs ABI for idxd driver

Add the sysfs ABI information for idxd driver in
Documentation/ABI/stable directory.

Signed-off-by: Jing Lin <jing.lin@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/157965025170.73301.13428570530450446901.stgit@djiang5-desk3.ch.intel.com


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