Allow ECDSA PK Opaque keys for ECDH Derivation

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
diff --git a/library/pk.c b/library/pk.c
index 7f4d5fe..3b42799 100644
--- a/library/pk.c
+++ b/library/pk.c
@@ -735,8 +735,10 @@
     /* prepare the key attributes */
     psa_set_key_type( &attributes, key_type );
     psa_set_key_bits( &attributes, bits );
-    psa_set_key_usage_flags( &attributes, PSA_KEY_USAGE_SIGN_HASH );
+    psa_set_key_usage_flags( &attributes, PSA_KEY_USAGE_SIGN_HASH |
+                                          PSA_KEY_USAGE_DERIVE);
     psa_set_key_algorithm( &attributes, PSA_ALG_ECDSA(hash_alg) );
+    psa_set_key_enrollment_algorithm( &attributes, PSA_ALG_ECDH );
 
     /* import private key into PSA */
     if( PSA_SUCCESS != psa_import_key( &attributes, d, d_len, key ) )