This commit allows switching SDK firmware:
nonos-sdk-pre-v3 shipped with release 2.5.0 has issues:
* Some boards show erratic behavior (radio connection is quickly lost), with an unknown cause.
These boards work well with previous nonos-sdk-2.2.1 firmware (#5736)
* Overall performances seem to have decreased (#5513)
This PR restores sdk2.2.1 (as in core-2.4.2).
SDK-pre-3.0 - which has brought long awaited fixes (WiFi sleep modes) - is still available through a menu option available only with generic board.
BREAKING
* new define `-DNONOSDK221=1` or `-DNONOSDK3V0=1`
* for external build systems: new library directory: `tools/sdk/lib/<version>/lib`
* PIO: variable `PIO_FRAMEWORK_ARDUINO_ESPRESSIF_SDK3` is needed for sdk-pre-v3.
Fix#5736
