multimedia/onevpl: Deprecate and set to expire on 2026-09-30

Upstream has been renamed to libvpl and libvpl-tools. Use
multimedia/libvpl and multimedia/libvpl-tools.

While here, add CONFLICTS_INSTALL=libvpl.

PR: 293561
Reported by: Yuichiro NAITO <naito.yuichiro@gmail.com>