docs/gpu: add entry for VaAPI

This CL adds a vaapi.md entry to docs/gpu, explaining how to trace its
cpu/memory/power consumption, and to verify/debug its installation.

Bug: 912295, 514914
Change-Id: Ieb7ad033e20f1211a9ae170af9378296a58c0689
Reviewed-on: https://chromium-review.googlesource.com/c/1383147
Commit-Queue: Miguel Casas <mcasas@chromium.org>
Reviewed-by: Andres Calderon Jaramillo <andrescj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#618265}
1 file changed