This allows DRI3 to pick between UIF and raster according to whether we're
pageflipping or not and whether the pageflipping display can do UIF,
avoiding copies for the windowed/composited case that previously was
forced to linear.

Improves windowed glmark2 -b build:use-vbo=false performance by 30.7783%
+/- 13.1719% (n=3)