iio: accel: adxl345: add double tap feature

iio: accel: adxl345: add double tap feature

Add the double tap feature of the sensor. The interrupt handler needs
to catch and forward the event to the IIO channel. The single tap
implementation now is extended to deal with double tap as well.

Doubletap introduces window and latency times, both in us. Since both
times are scaled, the 8-bit register value is stored in hardware,
where the scaled value in [us] is stored as member variable.

Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
Link: https://patch.msgid.link/20250414184245.100280-4-l.rubusch@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>