crypto: scatterwalk - Add scatterwalk_crypto_chain helper

A lot of crypto algorithms implement their own chaining function.
So add a generic one that can be used from all the algorithms that
need scatterlist chaining.

Signed-off-by: Steffen Klassert <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

include/crypto/scatterwalk.h

···
 	return (++sg)->length ? sg : (void *)sg_page(sg);
 }
 
+static inline void scatterwalk_crypto_chain(struct scatterlist *head,
+					    struct scatterlist *sg,
+					    int chain, int num)
+{
+	if (chain) {
+		head->length += sg->length;
+		sg = scatterwalk_sg_next(sg);
+	}
+
+	if (sg)
+		scatterwalk_sg_chain(head, num, sg);
+	else
+		sg_mark_end(head);
+}
+
 static inline unsigned long scatterwalk_samebuf(struct scatter_walk *walk_in,
 						struct scatter_walk *walk_out)
 {