coresight: trbe: Save and restore state across CPU low power state

coresight: trbe: Save and restore state across CPU low power state

TRBE context can be lost when a CPU enters low power states.  If a trace
source is restored while TRBE is not, tracing may run without an active
sink, which can lead to hangs on some devices (e.g., Pixel 9).

The save and restore flows are described in the section K5.5 "Context
switching" of Arm ARM (ARM DDI 0487 L.a). This commit adds save and
restore callbacks with following the software usages defined in the
architecture manual.

During the restore flow, since TRBLIMITR_EL1.E resets to 0 on a warm
reset, the trace buffer unit is disabled when idle resume, it is safe to
restore base/pointer/status registers first and program TRBLIMITR_EL1
last.

Signed-off-by: Yabin Cui <yabinc@google.com>
Co-developed-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Reviewed-by: James Clark <james.clark@linaro.org>
Tested-by: James Clark <james.clark@linaro.org>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Tested-by: Jie Gan <jie.gan@oss.qualcomm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20260515-arm_coresight_path_power_management_improvement-v14-25-f88c4a3ecfe9@arm.com