st_lsm6dsx: support trigger/buffer iio api for the lsm9ds1

we currently require userspace to repeatedly read the accelerometer. We need to support the interrupt-based mode: configure the device for interrupts and implement iio trigger/buffer support for userspace.

iio-sensor-proxy should be ready for it: https://gitlab.freedesktop.org/hadess/iio-sensor-proxy/-/blob/master/src/drv-iio-buffer-accel.c#L168