ioat: kill function prototype ifdef guards

The only .c files that utilize these protected prototypes depend on
CONFIG_INTEL_IOATDMA=y, so there is no value gained in providing empty
prototypes.

[ Impact: pure cleanup ]

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