Drop txx9dmac's use of tx_list from struct dma_async_tx_descriptor in
preparation for removal of this field.

Cc: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

This patch adds support for the integrated DMAC of the TXx9 family.
Signed-off-by: NAtsushi Nemoto <anemo@mba.ocn.ne.jp>
Acked-by: NDan Williams <dan.j.williams@intel.com>
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>