iio: st_sensors: split open-drain parameters for irq1 and irq2

Define st_sensor_int_drdy structure in st_sensor_data_ready_irq in order
to contain irq line parameters of the device.
Moreover separate data-ready open-drain configuration parameters for INT1
and INT2 pins in st_sensor_data_ready_irq data structure.
That change will be used to properly support LIS3DHH accel sensor.

Signed-off-by: Lorenzo Bianconi <lorenzo.bianconi@st.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>