ARM: dts: msm: define standalone flag for rpm-smd driver node

Define standalone flag until real silicon comes. This flag allow RPM
driver to run in standalone mode irrespective of RPM channel presence.

Change-Id: Ib351f70526a4a82cf63b53ad2ea68fa911a69a5c
Signed-off-by: Archana Sathyakumar <asathyak@codeaurora.org>