dt-bindings: thermal: Add dt binding for QCOM LMh

Add dt binding documentation to describe Qualcomm
Limits Management Hardware node.

Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210809191605.3742979-8-thara.gopinath@linaro.org