dt-bindings: remoteproc: qcom,msm8916-mss-pil: Add MSM8974

The "qcom,msm8974-mss-pil" binding is still similar enough to MSM8916
to be covered by the same DT schema. The only difference is the
additional "mss-supply", which can be easily handled using a single
if statement.

Signed-off-by: Stephan Gerhold <stephan.gerhold@kernkonzept.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20220908182433.466908-4-stephan.gerhold@kernkonzept.com