power: qcom-charger: add support for internal and external rsense

USBIN-USBIN parallel configuration can have either an internal current
sensing via main charger's BATFET or an external current sense resistor.
The FCC split between main and parallel charger differs based on current
sensing mode, add support to differentiate internal/external sensing and
the FCC split is done as follows:
- Internal Sensing: Main charger configure to full FCC
		    Parallel charger configured to 50% FCC.
- External sensing: Main charger configure to 50% FCC
		    Parallel charger configured to 50% FCC.

Change-Id: Ia0c6234ce6f62af460edd3c4f56e34810899b3e3
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>