ARM: dts: qcom: pm8226: add IADC node

Add a node for the current ADC (IADC) found in PM8226.

Signed-off-by: Rayyan Ansari <rayyan@ansari.sh>
[bjorn: Updated node name and added specific compatible, per request from Luca Weiss]
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221223193403.781355-4-rayyan@ansari.sh