dt-bindings: clock: qcom,sa8775p-gcc: add the power-domains property

The binding document is missing the power-domains property. Add it and
update the example.

Fixes: 0fff9fa0 ("dt-bindings: clock: Add Qualcomm SA8775P GCC")
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230130145154.195562-1-brgl@bgdev.pl