mbedtls: add wrapper for mbed hw poll

This wrapper uses RNG HAL API

Author: 0xc0170

features/mbedtls/mbed/wrapper.c

@@ -0,0 +1,29 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2016 ARM Limited
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "hal/rng_api.h"
+
+#if defined(MBEDTLS_ENTROPY_HARDWARE_ALT) && defined(DEVICE_RNG)
+
+int mbedtls_hardware_poll( void *data, unsigned char *output, size_t len, size_t *olen ) {
+    rng_t rng_obj;
+    rng_init(&rng_obj);
+    int ret = rng_get_numbers(&rng_obj, output, len, olen);
+    rng_free(&rng_obj);
+    return ret;
+}
+
+#endif