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

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: I1403f6bc2546efa8155b8fbb178d903109408067
Signed-off-by: Odelu Kukatla <okukatla@codeaurora.org>