esp32: Refactor backtrace and add esp_backtrace_print()

This commit refactors backtracing within the panic handler so that a common
function esp_backtrace_get_next_frame() is used iteratively to traverse a
callstack.

A esp_backtrace_print() function has also be added that allows the printing
of a backtrace at runtime. The esp_backtrace_print() function allows unity to
print the backtrace of failed test cases and jump back to the main test menu
without the need reset the chip. esp_backtrace_print() can also be used as a
debugging function by users.

- esp_stack_ptr_is_sane() moved to soc_memory_layout.h
- removed uncessary includes of "esp_debug_helpers.h"

components/esp32/gdbstub.c

@@ -22,8 +22,8 @@
 #include "esp32/rom/ets_sys.h"
 #include "soc/uart_periph.h"
 #include "soc/gpio_periph.h"
+#include "soc/soc_memory_layout.h"
 #include "esp_private/gdbstub.h"
-#include "esp_debug_helpers.h"
 #include "driver/gpio.h"
 #include "freertos/FreeRTOS.h"
 #include "freertos/task.h"