ARM: dts: msm: Add support for UART console on sdxprairie target

Add devicetree node to bringup UART console on sdxprairie target for
logs and executing shell commands.

Change-Id: I1b6fd500769843c8f87a50d0d8255e52a18229bb
Signed-off-by: Jeevan Shriram <jshriram@codeaurora.org>