coresight: Move per-CPU source pointer to core layer

coresight: Move per-CPU source pointer to core layer

Move the per-CPU source pointer from ETM perf to the core layer, as this
will be used for not only perf session and also for CPU PM notifiers.

Provides coresight_{set|clear|get}_percpu_source() helpers to access the
per-CPU source pointer. Add a raw spinlock to protect exclusive access.

Device registration and unregistration call the set and clear helpers
for init and teardown the pointers.

Update callers to invoke coresight_get_percpu_source() for retrieving
the pointer.

Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Reviewed-by: James Clark <james.clark@linaro.org>
Tested-by: James Clark <james.clark@linaro.org>
Tested-by: Jie Gan <jie.gan@oss.qualcomm.com>
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/20260515-arm_coresight_path_power_management_improvement-v14-9-f88c4a3ecfe9@arm.com