The ioat library currently only supports DMA copy operations, but the
hardware can do other types of transfers. Add a union of the hardware
descriptor structures to enable support for the other operations in the
future.
Also add a generic hardware descriptor type to allow access to the parts
of the descriptor that are common between all types.
Change-Id: I3b54421ce771f58b78910e790b53026f311f918e
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>