arm64: dts: qcom: pm8998: Add pm8998 thermal zone

The thermal zone uses spmi-temp-alarm as sensor, the trip points
correspond to the PMIC thermal stages 1 and 2. The critical trip
point at 125°C disables the partial PMIC shutdown at stage 2.

Without an IIO input the sensor only reports a limited number of
temperatures:

- 37°C for temperatures below 105°C
- 107°C for temperatures >= 105°C and < 125°C
- 127°C for temperatures >= 125°C

(the numbers correspond to a stage 1 threshold of 105°C)

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>