power: qcom-step-chg: Add a new file for step-charging

Add a new file which manages the step charging solution.
It supports 2 sources for step-charging - VBATT and SOC.
The solution samples the VBATT/SOC periodically and
applies the FCC from a static look-up table.

Change-Id: I82f560df5a6a8ad0cd46e989f9944d93cb5529d7
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>