linuxkpi: acpi/video.h: Add stubs acpi_video_{register,unregister}

Needed by i915.

Reviewed by: bz
Obtained from: drm-kmod
Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D36102

(cherry picked from commit afe53d7f7a9cf09c7443a979ac46f463c8f1cb17)