arm: dts: msm8974: thermal: Add "qcom,sensors" property

This new property allows the number of sensors to be configured from DT
instead of being hardcoded in platform data. Use it.

Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>