dt-bindings: soc: qcom: smd-rpm: Document SM6125 compatible

Add the SM6125 compatible to the documentation

Signed-off-by: Martin Botka <martin.botka@somainline.org>
Link: https://lore.kernel.org/r/20210523211556.731976-3-martin.botka@somainline.org


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>