dmaengine: idxd: expose general capabilities register in sysfs

There are some capabilities for the device that are interesting to user
apps that are interacting directly with the device. Expose gencap register
in sysfs to allow that information.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/158256729399.55526.10842505054968710547.stgit@djiang5-desk3.ch.intel.com


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