Keys may allow a second algorithm

Add a second permitted algorithm to key policies.

This commit includes smoke tests that do not cover psa_copy_key.
diff --git a/include/psa/crypto_struct.h b/include/psa/crypto_struct.h
index ee3ecd7..8850357 100644
--- a/include/psa/crypto_struct.h
+++ b/include/psa/crypto_struct.h
@@ -228,9 +228,10 @@
 {
     psa_key_usage_t usage;
     psa_algorithm_t alg;
+    psa_algorithm_t alg2;
 };
 
-#define PSA_KEY_POLICY_INIT {0, 0}
+#define PSA_KEY_POLICY_INIT {0, 0, 0}
 static inline struct psa_key_policy_s psa_key_policy_init( void )
 {
     const struct psa_key_policy_s v = PSA_KEY_POLICY_INIT;