i965: Drop a special case for guessing small miptree levels.

i965: Drop a special case for guessing small miptree levels.

Let's say you started allocating your 2D texture with level 2 of a tree as
a 1x1 image.  The driver doesn't know if this means that level 0 is 4x4 or
4x1 or 1x4, so we would just allocate a single 1x1 and let it get copied
in to the real location at texture validate time later.

Since this is just a temporary allocation that *will* get copied, the
extra space allocation of just taking the normal path which will happen to
producing a 4x1 level 0, 2x1 level 1, and 1x1 level 2 is the right way to
go, to reduce complexity in the normal case.

No change in miptree copies over the course of a piglit run.

Reviewed-by: Chad Versace <chad.versace@linux.intel.com>