hwmon: adc: Add ADC driver snapshot

Voltage ADC (VADC) and Current ADC (IADC) drivers
are used by clients to measure ADC such as voltage
phone power, thermistors and battery current.

This snapshot is taken as of msm-4.4
'commit <4f1f60e00d6a> ("Merge "ARM: dts:
msm: add nt35597 sharp panel node for sdm660"")'.

Change-Id: Ied07c12476916c181211d101786adffc2f762840
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>