dt-bindings: soc: qcom: qcom,pmic-glink: document SM8550 compatible

Document the SM8550 compatible used to describe the pmic glink
on this platform.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230130-topic-sm8450-upstream-pmic-glink-v5-3-552f3b721f9e@linaro.org