dmaengine: ioatdma: fix zero day warning on incompatible pointer type

The 32bit build is creating this warning. Since we don't expect anyone
actually use this on 32bit, restrict ioatdma to be built only on x86_64.
This issue has long existed and only reason it's surfacing due to code
refactoring.

   drivers/dma/ioat/dma.c: In function 'ioat_timer_event':
>> drivers/dma/ioat/dma.c:870:39: warning: passing argument 2 of 'ioat_cleanup_preamble' from incompatible pointer type
     if (ioat_cleanup_preamble(ioat_chan, &phys_complete))
                                          ^
   drivers/dma/ioat/dma.c:577:13: note: expected 'u64 *' but argument is of type 'dma_addr_t *'
    static bool ioat_cleanup_preamble(struct ioatdma_chan *ioat_chan,
                ^

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>