sensors: lsm6dsv16x: add RTIO async and fifo stream

Add RTIO async and RTIO stream functionalities that enables,
among all the other things, the sensor data streaming from FIFO.

RTIO stream is using both SENSOR_TRIG_FIFO_WATERMARK and
SENSOR_TRIG_FIFO_FULL triggers. The decoder currently only supports
following FIFO tags:

  - LSM6DSV16X_XL_NC_TAG
  - LSM6DSV16X_GY_NC_TAG
  - LSM6DSV16X_TEMP_NC_TAG

Following FIFO parameters has to be defined in device tree to
correctly stream sensor data:

  - fifo-watermark (defaults to 32)
  - accel-fifo-batch-rate (defaults to LSM6DSV16X_DT_XL_NOT_BATCHED)
  - gyro-fifo-batch-rate (defaults to LSM6DSV16X_DT_GY_NOT_BATCHED)
  - temp-fifo-batch-rate (defaults to LSM6DSV16X_DT_TEMP_NOT_BATCHED)

Signed-off-by: Armando Visconti <armando.visconti@st.com>