drivers/sensor: lsm6dsv16x: fix DT configuration read for int1/int2

Since lsm6dsv16x may be multi-instantiated, triggers must be enabled
and configured on DT basis and not only thru CONFIG_LSM6DSV16X_TRIGGER
macro; if either int1-gpios of int2-gpios (or both) are configured
in DT, the flag trig_enable is set to 'true' for that instance.
The previous implentation was lacking the check of those two Device
Tree properties, so trig_enabled was always true for all instances.

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