EM/Battery: Implement ADC sensor reading for charger

EM/Battery: Implement ADC sensor reading for charger

BZ: 15402

Implementation to fetch ADC sensor reading for obtaining adc channel
values in charger driver

Change-Id: If7800da1c6f145facaaf350cc39fac886c011f85
Signed-off-by: Amar Shankar <amarx.shankar@intel.com>
Reviewed-on: http://android.intel.com:8080/43226
Reviewed-by: Pujol, BenjaminX <benjaminx.pujol@intel.com>
Tested-by: P, Eshwar N <eshwar.n.p@intel.com>
Reviewed-by: Tc, Jenny <jenny.tc@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>