ARM: dts: qcom: msm8974: Add RPMCC DT node

Add the RPM Clock Controller DT node for msm8974-based platforms, so that
drivers can use the clocks provided by the RPM processor.

Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>