perf auxtrace: Add auxtrace_synth_id_range_start() helper

perf auxtrace: Add auxtrace_synth_id_range_start() helper

To avoid hardcoding the offset value for synthetic event IDs
in multiple auxtrace modules (arm-spe, cs-etm, intel-pt, etc.),
and to improve code reusability, this patch unifies
the handling of the ID offset via a dedicated helper function.

Signed-off-by: tanze <tanze@kylinos.cn>
Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>
Tested-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>