Changes:
KConfig: The option CONFIG_ESP32_RTCDATA_IN_FAST_MEM is added in Kconfig file for esp32 component.
esp32.common.ld: added support of RTC_DATA_ATTR, RTC_RODATA_ATTR data placement into appropriate segment according to Kconfig option.
esp32.ld: linker script is modified to set alias for memory segment selected by Kconfig option to place data. The segments for force placement are added for RTC_FAST_ATTR, RTC_SLOW_ATTR attributes.
esp_attr.h: added new attributes RTC_FAST_ATTR, RTC_SLOW_ATTR for force placement into fest/slow memory.
test_rtc_fast.c: Added unit test cases to check data placement into appropriate memory segment.
Updated documentation for RTC_DATA_ATTR, RTC_FAST_ATTR, RTC_SLOW_ATTR in deep_sleep_stub.rst file.
TW#18001
Closes https://github.com/espressif/esp-idf/issues/1553
We reserve 4KB Slow RTC memory to save RF calibation result and BT NVS data.
If not all these Slow RTC momory Blocks are used, we will open the other parts.
App can contain a stub program resident in RTC fast memory. Bootloader
will load the stub on initial boot. If the device wakes from deep sleep,
the stub is run immediately (before any other data is loaded, etc.)
To implement a custom wake stub, implement a function in your program:
```
void RTC_IRAM_ATTR esp_wake_deep_sleep(void)
{
esp_default_wake_deep_sleep();
// other wake logic
}
```
... and it will replace the default implementation.
