drivers/sensor: iis2dlpc: Move trigger pulse Kconfig property into DT

Move iis2dlpc trigger pulse configurations from Kconfigs to Device Tree.
Moreover the dts properties have been renamed as 'tap', which sounds a
better name to immediately catch the feature behind it. Since tap
threshold cannot be zero, this value (which is the default in dts
binding) is used to enable/disable the device feature per each axis.
The event can be generated on INT1 only.

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