crypto: caam - replace sg_count() with sg_nents_for_len()

Replace internal sg_count() function and the convoluted logic
around it with the standard sg_nents_for_len() function.
src_nents, dst_nents now hold the number of SW S/G entries,
instead of the HW S/G table entries.

With this change, null (zero length) input data for AEAD case
needs to be handled in a visible way. req->src is no longer
(un)mapped, pointer address is set to 0 in SEQ IN PTR command.
Signed-off-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/caam/sg_sw_sec4.h

@@ -73,14 +73,3 @@ static inline struct sec4_sg_entry *sg_to_sec4_sg_len(
 	} while (total);
 	return sec4_sg_ptr - 1;
 }
-
-/* derive number of elements in scatterlist, but return 0 for 1 */
-static inline int sg_count(struct scatterlist *sg_list, int nbytes)
-{
-	int sg_nents = sg_nents_for_len(sg_list, nbytes);
-
-	if (likely(sg_nents == 1))
-		return 0;
-
-	return sg_nents;
-}