arm64: dts: qcom: msm8998: Add rpmpd node

Add the rpmpd node on the msm8998 and define the available levels.

Reviewed-by: Jeffrey Hugo <jhugo@codeaurora.org>
Reviewed-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sibi Sankar <sibis@codeaurora.org>
[bjorn: dropped use of level defines, to allow merging in parallel]
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

Signed-off-by: Andy Gross <agross@kernel.org>