esp32: SEGGER SystemView Tracing Support

Implements support for system level traces compatible with SEGGER
SystemView tool on top of ESP32 application tracing module.
That kind of traces can help to analyse program's behaviour.
SystemView can show timeline of tasks/ISRs execution, context switches,
statistics related to the CPUs' load distribution etc.

Also this commit adds useful feature to ESP32 application tracing module:
 - Trace data buffering is implemented to handle temporary peaks of events load

components/freertos/include/freertos/task.h

@@ -1297,6 +1297,25 @@ char *pcTaskGetTaskName( TaskHandle_t xTaskToQuery ) PRIVILEGED_FUNCTION; /*lint
  */
 UBaseType_t uxTaskGetStackHighWaterMark( TaskHandle_t xTask ) PRIVILEGED_FUNCTION;
 
+/**
+ * task.h
+ * <PRE>uint8_t* pxTaskGetStackStart( TaskHandle_t xTask);</PRE>
+ *
+ * INCLUDE_pxTaskGetStackStart must be set to 1 in FreeRTOSConfig.h for
+ * this function to be available.
+ *
+ * Returns the start of the stack associated with xTask.  That is,
+ * the highest stack memory address on architectures where the stack grows down
+ * from high memory, and the lowest memory address on architectures where the
+ * stack grows up from low memory.
+ *
+ * @param xTask Handle of the task associated with the stack returned.
+ * Set xTask to NULL to return the stack of the calling task.
+ *
+ * @return A pointer to the start of the stack.
+ */
+uint8_t* pxTaskGetStackStart( TaskHandle_t xTask) PRIVILEGED_FUNCTION;
+
 /* When using trace macros it is sometimes necessary to include task.h before
 FreeRTOS.h.  When this is done TaskHookFunction_t will not yet have been defined,
 so the following two prototypes will cause a compilation error.  This can be