interconnect: qcom: Add interconnect RPM over SMD driver

On some Qualcomm SoCs, there is a remote processor, which controls some of
the Network-On-Chip interconnect resources. Other CPUs express their needs
by communicating with this processor. Add a driver to handle communication
with this remote processor.

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