power: Add STC3117 Fuel Gauge driver

Linux driver for STC3117 battery monitoring IC from
STMicroelectronics.

Git-commit:	47b14a831a4e89b6ef62bffd95f26d7d8fbeea1d
Git-repo: https://github.com/st-sw/STGasGaugeLinuxDrivers


[aghayal@codeaurora.org: Fixed trivial merge conflicts,
compilation errors and updated the commit text]

Change-Id: I4fcbd2fb06f2869253bd5aa500d5fb6a42caf31b
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>