arm64: dts: qcom: pm8994: Add VADC node

Add VADC note and some of its channels to allow
for voltage/temperature reading.

Signed-off-by: Konrad Dybcio <konradybcio@gmail.com>
Link: https://lore.kernel.org/r/20201005150313.149754-2-konradybcio@gmail.com


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>