softpipe: use the polygon stipple utility module

softpipe: use the polygon stipple utility module

This is an alternative to the draw module's polygon stipple stage.
The softpipe implementation here is just a test.  The advantange of
using the new polygon stipple utility module (with other drivers)
is we can avoid software vertex processing in the draw module and
get much better performance.
Polygon stipple doesn't require special vertex processing like
the other draw module stage.