arm64: dts: qcom: sdm845: mtp: Add vadc channels and thermal zones

Downstream defines four ADC channels related to thermal sensors external
to the PM8998 and two channels for internal voltage measurements.

Add these to the upstream SDM845 MTP, describe the thermal monitor
channels and add thermal_zones for these.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Vinod Koul <vkoul@kernel.org>
Link: https://lore.kernel.org/r/20211005032531.2251928-5-bjorn.andersson@linaro.org