Coresight: Allocate trace ID after building the path

The trace_id will be stored in coresight_path instead of being declared
everywhere and allocated after building the path.

Co-developed-by: James Clark <james.clark@linaro.org>
Signed-off-by: James Clark <james.clark@linaro.org>
Signed-off-by: Jie Gan <quic_jiegan@quicinc.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20250303032931.2500935-6-quic_jiegan@quicinc.com