perf script: Add not taken event for branch stack

The branch stack has an existed field for printing mispredict, extend
the field for printing events and add support not-taken event.

Reviewed-by: Ian Rogers <irogers@google.com>
Reviewed-by: James Clark <james.clark@linaro.org>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Link: https://lore.kernel.org/r/20250304111240.3378214-6-leo.yan@arm.com


Signed-off-by: Namhyung Kim <namhyung@kernel.org>