iio: accel: adxl372: factor out buffer and trigger setup

iio: accel: adxl372: factor out buffer and trigger setup

Extract the triggered buffer, trigger allocation, and IRQ request
logic from adxl372_probe() into a dedicated adxl372_buffer_setup()
helper. This reduces the probe function complexity and prepares for
conditionally disabling buffer support on device variants with
known FIFO issues.

No functional change intended.

Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>