i965: Add support for XYUV format

Hi, This 3 patch series adds support for handling XYUV buffers. In terms of organization, this patch series is very similar to Lionel Landwerlin's series that added support for AYUV.

XYUV format was tested by having the Vivid (Virtual Video) driver generate the buffers that were captured as a dmabuf by weston-simple-dmabuf-v4l and sent to the Weston compositor to be displayed.