drivers/sensor: add Kconfig.trigger_template

Add Kconfig.trigger_template to allow an extensive re-use of
trigger configuration inside all sensor drivers.

This template must be included as in the following example:

    module = LSM6DSO
    thread_priority = 10
    thread_stack_size = 1024
    source "drivers/sensor/Kconfig.trigger_template"

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