EVEA H.264: Disable periodic key frames by default.

The V4L2 default GOP size is only 12. This inserts intra frames too frequently and wastes bitrate. In practice it is not necessary for encoder to send periodic key frames.

BUG=284783
TEST=verify that EVEA only produces one I-frame initially and then all P-frames after.
R=fischman@chromium.org, sheu@chromium.org

Review URL: https://codereview.chromium.org/24667002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225284 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225284