power: qpnp-charger: double check BAT_THERM voltage in BTC_HOT irq

BTC_HOT interrupt might be triggered by glitches on BAT_THERM pin and
causes charging stopped unexpected.

Using VADC to sample the voltage on BAT_THERM pin when BTC_TEMP_OK
interrupt triggered and BAT_TEMP_STATUS is HOT. If HOT_THD is set
to 35% of the VREF_BAT_THM, and the voltage sampled on BATT_THERM
is higher than HOT_THD, override BTC VCP_DET comparator and toggle
HOT_THD setting to 25% to take charging back immediately.

CRs-Fixed: 685765
Change-Id: I83b3d2b8eb430be20418ba0b58c0eb8d7b8f22ec
Signed-off-by: Chunmei Cai <ccai@codeaurora.org>