ARM: dts: msm: Add SSR support for MDM9x50

Enable ssr feature in RmNet for MDM9x50,
as per the new requirement.

Change-Id: If0457e86f03da1f1f268a915c6f9d750d182eebf
Acked-by: Mohammed Javid <mjavid@qti.qualcomm.com>
Signed-off-by: Utkarsh Saxena <usaxena@codeaurora.org>