soc: qcom: smd-rpm: Add msm8998 compatible

Add the compatible for the RPM in MSM8998, so that rpm resources can be
made available.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>