iio: accel: adxl313: add AC coupled activity/inactivity events

iio: accel: adxl313: add AC coupled activity/inactivity events

Introduce AC-coupled activity and inactivity as MAG_ADAPTIVE events.
This adds a new set of threshold and duration configuration options,
ensures proper handling of event disabling, and extends the use of the
link bit to support complementary event configurations.

For example, either ACTIVITY or ACTIVITY_AC can be enabled, but only the
most recently set configuration will remain active. Disabling ACTIVITY
will have no effect if ACTIVITY_AC is currently enabled, as the event
types must match (i.e., ACTIVITY_AC must be explicitly disabled). When
either INACTIVITY or INACTIVITY_AC is enabled alongside an activity
event, the link bit is set.

With the link bit and auto-sleep enabled, activity and inactivity events
represent changes in the sensor's power-saving state and are only
triggered upon actual state transitions. Since AC coupling uses separate
bits for activity and inactivity, each can be configured independently.
For instance, ACTIVITY can be linked with INACTIVITY_AC.

If one of the linked events is disabled, the link bit is cleared. In
that case, the remaining event will no longer reflect a state transition
but will instead trigger based on periodic inactivity or whenever the
activity threshold is exceeded.

Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20250702230819.19353-8-l.rubusch@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>