ARM: dts: msm: Add proxy client node for sdm670

Proxy bus client is required to ensure that a certain
minimum state for a critical resource at the beginning
of boot up before the clients have probed and voted for
required state.

Change-Id: I6795fbbd360dd27e1237dd3dc3a905d3446e51ef
Signed-off-by: Odelu Kukatla <okukatla@codeaurora.org>