msm: msm_bus: Add Bus-RPM interface using RPM-SMD APIs

For MSM8974, communication to RPM is done through SMD.
For this new RPM-SMD driver APIs were introduced.
This patch enables bus driver to commit arbitration
data to RPM using the RPM-SMD APIs.
To maintain backward compatibility, the old RPM
communication file contains a stub for remote-init.

Change-Id: Ie32cec94b557c2d3b04be96a604e31c515817a54
Signed-off-by: Gagan Mac <gmac@codeaurora.org>