soc: qcom: jtagv8-etm: disable etm save and restore support

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.
Add support to disable save and restore functionality for ETM
registers based on a device tree property.

Change-Id: I3825b60d7eeef93e150b2c453e071336f3a92672
Signed-off-by: Sarangdhar Joshi <spjoshi@codeaurora.org>