hwmon: msm_adc: Calibrate HK/XOADC

Calibration for HK/XOADC is done once at init by
msm_adc before the first ADC reading is processed.

Calibration performed for every ADC read is expensive
and not recommended. Remove support to request
calibration by ADC clients.

Add stubs for pmic8058 xoadc functions to fix
featurization

Change-Id: I7f0e165bddaa49c5daf33df5ed77428ccc1434c5
Signed-off-by: Vijayakumar Muthuvel Manickam <vmuthuve@codeaurora.org>