ARM: dts: msm: add rtb trace support for mdmfermium

Add RTB support to device tree node which enables RTB logging on
mdmfermium. 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: I5ea80f5e6284aae550e63231afe5fa18961c7190
Signed-off-by: Shaoqing Liu <shaoqingliu@codeaurora.org>