dmaengine: ioatdma: clean up local dma channel data structure

Kill the common ioatdma channel structure and everything that is not
dma_chan to be ioat_dma_chan. Since we don't have to worry about v1
and v2 ioatdma anymore this makes it much cleaner and obvious for
maintenance.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>