arm64: dts: qcom: sc8280xp-pmics: Add PMK8280 ADC7 block

Add support for ADC7 block available in PMK8280 for reading the
temperature via the AMUX pins.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@somainline.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221103095810.64606-6-manivannan.sadhasivam@linaro.org