dt-bindings: thermal: Add a property to account BCL threshold bit shift

Newer BCL hardware doesn't have the threshold registers bit shifted
compared to the ADC measurement register. Add a new flag
qcom,pmic7-threshold, which needs to be added for these new targets so
that the software driver will account for the bit shifting in the
threshold calculation.

Change-Id: I6bc33f14a2717e060c9d32d199df10cc269ca6f1