dmanegine: ioatdma: remove function ptrs in ioatdma_device

Since we are a "single" device driver now we no longer require the function
pointers in ioatdma_device. Remove.

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>