ioat: cleanup ->timer_fn() and ->cleanup_fn() prototypes

If the calling convention of ->timer_fn() and ->cleanup_fn() are unified
across hardware versions we can drop parameters to ioat_init_channel() and
unify ioat_is_dma_complete() implementations.

Both ->timer_fn() and ->cleanup_fn() are modified to expect a struct
dma_chan pointer.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>