ARM: dts: msm: Add rpm_bus node to mdmcalifornium devicetree

Add the rpm_bus node with the standalone flag so the RPM
clocks can be probed.

In the absence of fully functional SMD and RPM drivers
in a pre-sil environment, the standalone flag is required
to allow the RPM driver to run in standalone mode irrespective
of the actual RPM channel presence.

Change-Id: I2a7ec8efb52bb949090f5a5edf40de2a0d13a871
Signed-off-by: Devesh Jhunjhunwala <deveshj@codeaurora.org>