ARM: dts: msm: add apps watchdog entry for plutonium

Add watchodg to device tree entry to enable configuring the watchdog
timer to cause barks and bites so as to detect system hangs.

Change-Id: I780bc207d3de63f8271738bc087d605c35d642ed
Signed-off-by: Aparna Das <adas@codeaurora.org>