arm64: dts: qcom: sa8295p-adp: Add RTC node

The first PM8540 PMIC has an available RTC block, describe this in the
SA8295P ADP. Mark it as wakeup-source to allow waking the system from
sleep.

Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221205174309.16733-1-quic_bjorande@quicinc.com