thermal/debugfs: Make tze_seq_show() skip invalid trips and trips with no stats

Currently, tze_seq_show() output includes all of the trips in the zone
except for critical ones, including invalid trips and trips with no stats
which is confusing.

Make it skip the trips for which there is not mitigation information.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>