power: smb349-charger: update interrupt handling

It was observed that once USB is inserted and apsd complete interrupt
triggers, the driver does not update the battery power supply. Change
the driver to update the battery power supply when USB insertion
happens.

Take this opportunity to update the interrupt handling code so that
diagnostic information on individual interrupt count could be retrieved
later.

While at it, provide I2C peek poke functionality - this comes handy for
debugging charging issues.

Change-Id: Id5f96efb8f6d41b64ad9243e0561d8598be81d97
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>