perf script: Add not taken event for branches

Some hardware (e.g., Arm SPE) can trace the not taken event for
branches.  Add a flag for this event and support printing it.

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/20250304111240.3378214-5-leo.yan@arm.com


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