i915: Use Y tiling for textures

i915: Use Y tiling for textures

This basically reverts commit
2acc7193743199701f8f6d1877a59ece0ec4fa5b.

With the previous change, we're not batchbuffer limited any
longer. So we actually start seeing a performance difference
between X and Y tiling. X tiling is funny because it is
faster for screen-aligned quads but slower in games. So let's
use Y tiling which is 10% faster overall.