intel: Fallback to meta if we're asked to CopyTexImage2D from RGB to RGBA

intel: Fallback to meta if we're asked to CopyTexImage2D from RGB to RGBA

The pixel transfer rules state that we must set alpha to 1.0 in this case
which we can't easily do with the blitter.  We can do to passes: one that
sets the alpha to 0xff and one that copies the RGB bits or we can just
use the 3D engine.  Neither approach seems worth it for this case.