swrast: Just use _EnabledCoordUnits for figuring out which texcoords to build.

swrast: Just use _EnabledCoordUnits for figuring out which texcoords to build.

_EnabledUnits is all of the first 32 image units that are used by fixed
function or programs, while _EnabledCoordUnits is just which fixed function
fragment shader texcoords need to be generated.  This is a theoretical bugfix
in the case of a vertex shader texturing from large texture image unit number
(we'd end up flagging something other than a VARYING_SLOT_TEXn as needing to
be generated), but it's actually just motivated by trying to kill
_EnabledUnits.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>