hwmon: qpnp-adc: Add scaling support for ADC channels

Add new scale function and mapping table for batt_therm.
Add scale function support for current channels and for
chg_temp,die_temp.

Change-Id: I3e00955db40f7699dc4740e6e56d4252a4013de4
Signed-off-by: Jishnu Prakash <jprakash@codeaurora.org>