Use pkg-config to find libva on Linux

Otherwise build can fail or not use the wanted libva version
when the gn arg use_vaapi is set to true (default is false).

Bug: 913118
Change-Id: I17c9199d032473bd10f45ae798e1ed4c2212a129
Reviewed-on: https://chromium-review.googlesource.com/c/1368950
Reviewed-by: Miguel Casas <mcasas@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Julien Isorce <julien.isorce@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616207}
2 files changed