arm64: dts: qcom: sa8775p: add the Power On device node

Add the PON node to PMIC #0 for sa8775p platforms.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230327125316.210812-9-brgl@bgdev.pl