sensors: add enable and poll_delay handle for stk3x1x sensor drver

Add enable and poll_delay handle functions for the stk3x1x light and
proximity sensor driver. The system will create the general enable and
poll_delay handles in the "/sys/class/sensors/xxx/" for each sensor
drvier which is using the sensor class driver.

Change-Id: Ib082d3bbc278ef5c75ae38b3e702f84a13bca7a8
Signed-off-by: Jie Cheng <rockiec@codeaurora.org>