lib: smf: mark as unstable

mark State Machine Framework API as unstable,
as it is now used by usb-c and hawkBit.

Signed-off-by: Fin Maaß <f.maass@vogl-electronic.com>

Author: maass-hamburg

include/zephyr/smf.h

@@ -18,7 +18,7 @@
 /**
  * @brief State Machine Framework API
  * @defgroup smf State Machine Framework API
- * @version 0.1.0
+ * @version 0.2.0
  * @ingroup os_services
  * @{
  */