ARM: dts: msm: Add proxy client node for SM6150

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: Ib1757ce45e44d7658d56e641a2c02291c787825f
Signed-off-by: Odelu Kukatla <okukatla@codeaurora.org>