hammerhead kernel: implement always on rgb led support

When offms is set to 0, configure a single point
duty cycle at the desired led brightness.

Change-Id: I93b61af52ee2f695035e7f5d78814251c8d1da8d
 msm8974-regulator.dtsi: adjust GFX regulator parameters

settings based on qcom documentation

Signed-off-by: Paul Reioux <reioux@gmail.com>