ARM: dts: msm: add rtb to device tree for krypton

Add support to device tree node to enable RTB logging on samarium.
RTB logging provides useful debug information by logging events to
uncached buffer which can be processed from ramdumps in case of device
reset

Change-Id: I437986d91b6172278b92e20fd227a49ca41d6cd8
Signed-off-by: Aparna Das <adas@codeaurora.org>