arm64: dts: qcom: pmk8550: always enable RTC PMIC device

There's no reason to keep the RTC disabled, it has been tested
and is functional on the SM8550 QRD and MTP boards.

Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230525-topic-sm8550-upstream-pm8550-lpg-dt-v4-3-a288f24af81b@linaro.org