arm64: dts: sdm845: Add rpmh-clk node

This adds the rpmh-clk node to sdm845 based on the examples in the
bindings.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>