sensors: lsm6dsv16x: Kconfig: Fix trigger mode

Select TRIGGER_GLOBAL_THREAD by default if rtio streaming is enabled,
and TRIGGER_NONE otherwise. This change prevents bad trigger configurations
like

    CONFIG_LSM6DSV16X_TRIGGER=y
    CONFIG_LSM6DSV16X_TRIGGER_NONE=y

which does not have any sense.

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