Add CONFIG_DEBUG_SG sg validation

Add a Kconfig entry which will toggle some sanity checks on the sg
entry and tables.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

include/asm-h8300/scatterlist.h

@@ -4,6 +4,9 @@
 #include <asm/types.h>
 
 struct scatterlist {
+#ifdef CONFIG_DEBUG_SG
+	unsigned long	sg_magic;
+#endif
 	unsigned long	page_link;
 	unsigned int	offset;
 	dma_addr_t	dma_address;