sensor: add driver for HTS221 sensor

Add driver for HTS221 temeprature and relative humidity sensor.

Datasheet:
	http://www.st.com/resource/en/datasheet/hts221.pdf

Interpreting humidity and temperature readings document:
	http://www.st.com/resource/en/technical_note/dm00208001.pdf



Change-Id: I1fee9d8372ad71b22bc85a60939c82f81569e135
Origin: Original
Signed-off-by: Bogdan Davidoaia <bogdan.m.davidoaia@intel.com>