ARM: dts: msm: disable save / restore of etm registers on msm8996

Memory mapped accesses for ETM registers are not supported on
MSM8996 V2 when OS lock is set and there seems to be some
stability issues while using system interface for ETM registers.
Disable save and restore functionality for ETM registers on
MSM8996 V2.

Change-Id: I7553a53e65919ba8874b465cd53e8b422d98b0d7
Signed-off-by: Sarangdhar Joshi <spjoshi@codeaurora.org>