ARM: dts: msm: add rtb to device tree for 8092

Add support to device tree node to enable RTB logging on mpq8092.
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: I5db4571933fd1ed1ee7d3ecf20a1c9c9b856d8a7
Signed-off-by: Vignesh Radhakrishnan <vigneshr@codeaurora.org>