multimedia/libva-intel-driver: deprecate due to dead upstream

https://github.com/intel/intel-vaapi-driver/commit/fd727a4e9cb8

Not blindly recommending multimedia/libva-intel-media-driver:
- lacks support for pre-Broadwell (Gen < 8) GPUs
- lacks VP9 decode on Skylake (Gen9)
- lacks VP9 encode on Kabylake (Gen9.5)

Deprecation is for existing users to exercise caution decoding videos
from untrusted sources since the vendor no longer promises security fixes.

(cherry picked from commit 4da2294f)