crypto: curve25519 - add kpp selftest

In preparation of introducing KPP implementations of Curve25519, import
the set of test cases proposed by the Zinc patch set, but converted to
the KPP format.
Signed-off-by: NArd Biesheuvel <ardb@kernel.org>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

crypto/testmgr.c

@@ -4317,6 +4317,12 @@ static const struct alg_test_desc alg_test_descs[] = {
 		.alg = "cts(cbc(paes))",
 		.test = alg_test_null,
 		.fips_allowed = 1,
+	}, {
+		.alg = "curve25519",
+		.test = alg_test_kpp,
+		.suite = {
+			.kpp = __VECS(curve25519_tv_template)
+		}
 	}, {
 		.alg = "deflate",
 		.test = alg_test_comp,