ARM: dts: msm: add instance id property to remote etm for msm8996

Add instance id property to remote ETM dt nodes for msm8996 to
prepare for combining the RPM/WCN/MODEM/AUDIO ETM drivers into a unified
remote processor ETM driver.

Change-Id: Icee1116016f80799374b59d328ca6417462b3c22
Signed-off-by: Shaoqing Liu <shaoqingliu@codeaurora.org>
Signed-off-by: Xiaogang Cui <xiaogang@codeaurora.org>