dt-bindings: remoteproc: qcom,msm8916-mss-pil: Add MSM8909

Document the "qcom,msm8909-mss-pil" compatible for the modem remote
processor on MSM8909. It is used pretty much exactly like the existing
one for MSM8916.

Signed-off-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20220908182433.466908-5-stephan.gerhold@kernkonzept.com