power: pm8921-bms: calculate rbatt only at resume

The battery resistance (rbatt) measurement can only happen when the
current consumption of the device goes very low. This implies that
rbatt should be checked for only while resuming.

Update the driver to check and measure for rbatt only during resume.
As a result separate the functions that read state of charge (soc)
parameters from rbatt parameters. Also note the battery temperature
right before suspend. This will be used for adjusting the rbatt based
on temperature.

Change-Id: I254833f437605d6d64dcd6159edb8440d08383db
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>