[Linux] Enabling Hardware Acceleration with Libva in linux-x86.

    This commit is not upstreamable.

    Currently, VAAPI only enabled for ChromeOS and Windows on
    upstream. Although the ChromeOS uses same libva API as
    common linux world, upstream refuesed to enable it for linux
    common with maintainence concern. Refer to
    "https://codereview.chromium.org/16430003/" for more details.

    Upstream confirm VAVDA will continue to be restricted to
    CrOS/X86 for dev & testing only and not for chromium road map.
    So we maintain it for Crosswalk and that will benifit
    linux with VAAPI installed and includes Tizen.