The Xtensa FreeRTOS port does not save the threadptr register when
doing a voluntary yield. This can result in a crash when multiple
tasks used the threadptr register and call "taskYIELD()".
This commit adds the threadptr register to the solicited stack frame.
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
