intr_event(9): update copyright

To reflect my work on the rewrite, which is in-part sponsored by
the FreeBSD Foundation.

I have also included a copyright entry for trhodes@, who wrote the patch
beginning this rewrite in PR 100803.

Reviewed by: imp, jhb, emaste
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D36935