swr/rast: support polygonmode point

swr/rast: support polygonmode point

Add support for polygonmode point in the binner.  This is done by
splitting BinPostSetupPoints from BinPoints, so the earlier call can be
called from BinTriangles.  Setup has already been done at the time
BinPostSetupPoints needs to be called.

This checkin just adds support in the rasterizer.  A separate checkin
will add the appropriate driver support.

v2: remove cc stable
v3: modified commit message and subject line

Reviewed-by: Bruce Cherniak <bruce.cherniak@intel.com>