Add comment to set/increment step functions

These functions are thread safe, but using them from within multiple
threads at the same time may not have the intended effect, given order
cannot be guaranteed. Also, standardise header comment formatting.

Signed-off-by: Paul Elliott <paul.elliott@arm.com>

tests/include/test/helpers.h

@@ -111,6 +111,11 @@ int mbedtls_test_get_line_no(void);
 
 /**
  * \brief           Increment the current test step.
+ *
+ * \note            Calling this function from within multiple threads at the
+ *                  same time is not recommended - whilst it is entirely thread
+ *                  safe, the order of calls to this function can obviously not
+ *                  be ensured, so unexpected results may occur.
  */
 void mbedtls_test_increment_step(void);
 
@@ -215,30 +220,35 @@ void mbedtls_test_fail(const char *test, int line_no, const char *filename);
 void mbedtls_test_skip(const char *test, int line_no, const char *filename);
 
 /**
- * \brief       Set the test step number for failure reports.
+ * \brief           Set the test step number for failure reports.
  *
- *              Call this function to display "step NNN" in addition to the
- *              line number and file name if a test fails. Typically the "step
- *              number" is the index of a for loop but it can be whatever you
- *              want.
+ *                  Call this function to display "step NNN" in addition to the
+ *                  line number and file name if a test fails. Typically the
+ *                  "step number" is the index of a for loop but it can be
+ *                  whatever you want.
+ *
+ * \note            Calling this function from a within multiple threads at the
+ *                  same time is not recommended - whilst it is entirely thread
+ *                  safe, the order of calls to this function can obviously not
+ *                  be ensured, so unexpected results may occur.
  *
  * \param step  The step number to report.
  */
 void mbedtls_test_set_step(unsigned long step);
 
 /**
- * \brief       Reset mbedtls_test_info to a ready/starting state.
+ * \brief           Reset mbedtls_test_info to a ready/starting state.
  */
 void mbedtls_test_info_reset(void);
 
 #ifdef MBEDTLS_TEST_MUTEX_USAGE
 /**
- * \brief       Get the test info data mutex.
+ * \brief           Get the test info data mutex.
  *
- * \note        This is designed only to be used by threading_helpers to avoid a
- *              deadlock, not for general access to this mutex.
+ * \note            This is designed only to be used by threading_helpers to
+ *                  avoid a deadlock, not for general access to this mutex.
  *
- * \return      The test info data mutex.
+ * \return          The test info data mutex.
  */
 mbedtls_threading_mutex_t *mbedtls_test_get_info_mutex(void);