dt-bindings: Add snapshot of RPM SMD devicetree binding

Add snapshot of RPM SMD devicetree binding to the
devicetree project.This snapshot is taken as of
'commit <f7835e76aab01> ("drivers: thermal: Add support
for RPM SMD cooling device")' of the msm-4.14 kernel project.

Change-Id: Ib2fd5196575d3ae9cfd0276f5e4beb7f9057f46d