Make entropy bias self test poll multiple times

Instead of polling the hardware entropy source a single time and
comparing the output with itself, the source is polled at least twice
and make sure that the separate outputs are different.
diff --git a/include/mbedtls/entropy.h b/include/mbedtls/entropy.h
index fb7f2f4..19e8e72 100644
--- a/include/mbedtls/entropy.h
+++ b/include/mbedtls/entropy.h
@@ -259,14 +259,14 @@
  */
 int mbedtls_entropy_self_test( int verbose );
 
-#if !defined(MBEDTLS_TEST_NULL_ENTROPY) && defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
+#if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
 /**
  * \brief          Checkup routine
  *
  * \return         0 if successful, or 1 if a test failed
  */
-int mbedtls_entropy_self_test_bias( int verbose );
-#endif /* !MBEDTLS_TEST_NULL_ENTROPY && MBEDTLS_ENTROPY_HARDWARE_ALT */
+int mbedtls_entropy_source_self_test( int verbose );
+#endif /* MBEDTLS_ENTROPY_HARDWARE_ALT */
 #endif /* MBEDTLS_SELF_TEST */
 
 #ifdef __cplusplus