arm64: dts: qcom: pm8998: Add adc node

This adds the adc node to pm8998 based on the examples in the
bindings. It also fixes the order of the included headers.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>