hwmon: qpnp-adc: Add PMIC 2.0 ADC bringup fixes

VADC/IADC peripheral is supported from PMIC 2.0 onwards.
Add version check to allow VADC/IADC reads if the
version is supported. Add probe defereal api for clients
who need to know if the ADC driver is ready. There is a
bug where the completion is not initialized. Fix it
by initializing it. Add support to disable the peripheral
after the ADC is read and enable it before starting a
conversion.

Add scaling functions to support reading the die temperature,
XO_THERM, batt_therm and batt_id. Add the ratiometric
calibration routine that uses the vref/gnd for calibration.
The ratiometric calibration is used for calibrating xo_therm,
batt_therm, batt_id.

Update the gain value used for calibration on the IADC
peripheral. PMIC 2.0 IADC peripheral uses 17.857mV instead
of 25mV for its gain calibration.

Change-Id: I2427a0106920557e95fa630554a26b974e4e4e39
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>