dmaengine: idxd: fix opcap sysfs attribute output

The operation capability register is 256bits. The current output only
prints out the first 64bits. Fix to output the entire 256bits. The current
code omits operation caps from IAX devices.

Fixes: c52ca478

 ("dmaengine: idxd: add configuration component of driver")
Reported-by: Lucas Van <lucas.van@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/161645624963.2003736.829798666998490151.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>