cnss: Migrate to upstream adc_tm interface for wlan vbat feature

Power voting need to be controlled based on the battery voltage,
Register ADC and IIO channels to monitor the battery voltage,
Register threshold notification with the ADC, to get voltage
change notification based on the configuration, Register IIO
channel to read current battery voltage, if the voltage is
exceeding the predefined threshold, then update the voltage
to the firmware using rpmsg command.

Change-Id: Ica61be1b0e823ca20c946599b639f7b18ce02e8b
Signed-off-by: Govind Singh <govinds@codeaurora.org>