arm64: dts: qcom: pm8550: add PWM controller

Add the PWM function to the pm8550 dtsi, this is usually used
to drive RGB leds on platforms using this PMIC.

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-v4-1-a288f24af81b@linaro.org