hwmon: pm8xxx-adc: Add HTC btm_threshold, pa_therm tables

* HTC uses custom functions to set these values, although they have set
  it to be the same value across their 8960/8064 lineup.
* Add alternate tables for HTC devices.

Change-Id: I6a90620ea5e53dc09b0b7d0e3153bc791d733cb8