power: battery: add support for override votes in FCC stepper

FCC stepper logic runtime calculates the step count based on the
current vote on Main and Parallel's FCC. However, in the case of
a override vote, the value of the overridden voter does not change
across steps and the step-FCC calculations are affected.

Hence update the FCC stepper logic to handle this condition by
tracking the override vote value.

Change-Id: Ie228f5a42ac6b788ac74446726a4f557079e246e
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>