graphics/drm-515-kmod: Update to drm_v5.15.160_2

This exports all symbols from the modules.
See https://github.com/freebsd/drm-kmod/commit/676098fb2f54827d8a2dc7375ceecf62c96d0d66
for the explaination.

Sponsored by: Beckhoff Automation GmbH & Co. KG