power: smb135x-charger: use ov/uv interrupts for insertion/removal

The current driver uses the status register 8 (0x4E) to confirm whether
there is a charger present or not. The voltage thresholds on which the
status register is updated are different from the voltage thresholds
when under/over voltage interrupts are triggered. Use uv/ov interrupts
to track charger insertion and removal.

Change-Id: I2250773d151c4fc0e47f2225ba36f52245932498
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>