coresight: etm3x: Always set tracer's device mode on target CPU

coresight: etm3x: Always set tracer's device mode on target CPU

The ETMv3 driver shares the same issue as ETMv4 regarding race
conditions when accessing the device mode.

This commit applies the same fix: ensuring that the device mode is
modified only by the target CPU to eliminate race conditions across
CPUs.

Fixes: 22fd532eaa0c ("coresight: etm3x: adding operation mode for etm_enable()")
Reviewed-by: Mike Leach <mike.leach@linaro.org>
Tested-by: James Clark <james.clark@linaro.org>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20251111-arm_coresight_power_management_fix-v6-3-f55553b6c8b3@arm.com