intel: Fall back to X-tiling when larger than estimated aperture size.

intel: Fall back to X-tiling when larger than estimated aperture size.

If a region is larger than the estimated aperture size, we map/unmap it
by copying with the BLT engine.  Which means we can't use Y-tiling.

Fixes Piglit max-texture-size and tex3d-maxsize, which regressed in my
recent change to use Y-tiling by default on Gen6+.  This was due to a
botched merge conflict resolution.

v2: Return a mask of valid tilings from intel_miptree_select_tiling.
    This allows us to avoid the X-tiling fallback if Y-tiling is actually
    mandatory.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>