arm64: dts: sm8150: Add rpmh power-domain node

Add the DT node for the rpmhpd power controller.

Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Rajendra Nayak <rnayak@codeaurora.org>
Signed-off-by: Sibi Sankar <sibis@codeaurora.org>
Link: https://lore.kernel.org/r/0101016e7f99eab9-35efa01f-8ed3-4a77-87e1-09c381173121-000000@us-west-2.amazonses.com


[bjorn: Use constant for opp6, until include lands]
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>