power: pm8921-charger: explicitly call bms for start/stop charging

The current code relies on charge state changes to check battery charging
and notify bms.  The charge state change interrupt can occur many times,
causing unnecessary checks on battery charging. Instead explicitly invoke
charging checks in case of events known to start/stop charging. On similar
lines disable the use of charge state change interrupts.

Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>