i386: enable sg chaining

We don't need to do more on x86, there's no iommu to be worried about.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

include/asm-x86/scatterlist_32.h

@@ -10,6 +10,8 @@ struct scatterlist {
     unsigned int	length;
 };
 
+#define ARCH_HAS_SG_CHAIN
+
 /* These macros should be used after a pci_map_sg call has been done
  * to get bus addresses of each of the SG entries and their lengths.
  * You should only work with the number of sg entries pci_map_sg