dmaengine: idxd: Merge definition of dsa_batch_desc into dsa_hw_desc

We don't need a special structure just for batch descriptors. The
layout matches the general form for other descriptors.

Merge the desc_list_addr field into the union of other aliases for
the the third quadword in the structure.

Create a union to alias "xfer_size" with "desc_count".

Signed-off-by: Tony Luck <tony.luck@intel.com>
Acked-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/158387868208.35922.5895104426944263789.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>