power: qpnp-linear-charger: add support for VDDMAX trimming

It is observed that in some cases battery does not charge
to configured VDD_MAX. Fix this by adding support for VDD_MAX
trimming. Trimming is applied at regular interval after battery
charging enters CV mode.

VDD_MAX trimming is applied when the following conditions are met:
Charger is in VDD loop, IBAT is between 0ma and -300ma and delta
between VDD_MAX and VBAT is above trimming threshold (13mV).

CRs-Fixed: 672374
Change-Id: I5b95c631ea1a93c940477d860c2aabbd482a2e98
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>