power: qcom: step-chg-jeita: Use a common struct for parameters

Step charging and SW JEITA algorithms use similar variables for
the parameters. Use a common struct to group it. This can be
leveraged later when different parameters can be passed from
the charger drivers.

Change-Id: I425a851728a603675f59cabc6a293593981ece25
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>