hwmon: qpnp-adc-current: Add periodic calibration

Support periodic IADC peripheral calibration to perform
calibration as a function of time and temperature.
Calibration is performed every 5 minutes and for
every 5degC temperature change in the die temperature.

As part of the periodic calibration update the USR trim
registers with fresh offset values. The clients can read
the offset trim values through their own trim registers.

Support reading internal RSENSE trim register and
use it for current calculation.

Also update the gain and offset api to support clients
who require the updated periodic calibrated values.

Change-Id: I2b3f0383b76417069333fb95c0c7fc1ac06eafd5
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>