i965: Set point rasterization rule to UPPER_RIGHT on Gen6-7.5.

i965: Set point rasterization rule to UPPER_RIGHT on Gen6-7.5.

Gen4-5 and Gen8+ already set this, but Gen6-7.5 did not.  We ought to
be consistent - the answer depends on the API, not the hardware generation.

The Sandybridge PRM says about RASTRULE_UPPER_RIGHT:

   "To match OpenGL point rasterization rules (round to +infinity, where
    this is the upper right direction wrt OpenGL screen origin of lower
    left).

So this is likely the one we should use.

Reviewed-by: Rafael Antognolli <rafael.antognolli@intel.com>