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

Add support to device tree node to enable RTB logging on msmzirc. 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: I331e3cb32c67a2336a21be4beb445baa811f881b
Signed-off-by: Sarangdhar Joshi <spjoshi@codeaurora.org>