input: sensor: add stk3x1x light/proximity sensor driver

Add Sensortek (formerly Sitronix) stk3x1x series ambient light and
proximity 3-in-1 sensor driver.

Change-Id: I88f76c1fdc57869b4113b6c27dcbccff979d78fa
Git-commit: c9f105c3ebba39131a037dd2ad8f81ce0f86e949
Git-repo: https://www.codeaurora.org/cgit/external/thundersoft/ihvjointlab/sensor-driver/


[bingzhec@codeaurora.org: added more detail to commit text]
Signed-off-by: Bingzhe Cai <bingzhec@codeaurora.org>
Signed-off-by: Pan Fang <fangpan@codeaurora.org>