power: qcom-charger: add support for USBIN-USBIN parallel configuration

Add support for USBIN-USBIN configuration based parallel charging. This
involves splitting Input Current Limit(ICL) between the main and the
parallel charger, ICL re-split is done when the settled AICL of the main
charger changes by 300mA.

Change-Id: I5b916f1503a2267ca1e73b24096cb60a304e3c19
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>