gen_key: limit EC key generation to when USE_PSA is disabled

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/programs/pkey/gen_key.c b/programs/pkey/gen_key.c
index 029558d..57b7d40 100644
--- a/programs/pkey/gen_key.c
+++ b/programs/pkey/gen_key.c
@@ -321,7 +321,7 @@
         }
     } else
 #endif /* MBEDTLS_RSA_C */
-#if defined(MBEDTLS_ECP_C)
+#if defined(MBEDTLS_ECP_C) && !defined(MBEDTLS_USE_PSA_CRYPTO)
     if (opt.type == MBEDTLS_PK_ECKEY) {
         ret = mbedtls_ecp_gen_key((mbedtls_ecp_group_id) opt.ec_curve,
                                   mbedtls_pk_ec(key),