swr/rast: Add KNOB_DISABLE_SPLIT_DRAW

swr/rast: Add KNOB_DISABLE_SPLIT_DRAW

This is useful for archrast data collection. This greatly speeds up the
post processing script since there is significantly less events generated.

Finally, this is a simpler option to communicate to users than having
them directly adjust MAX_PRIMS_PER_DRAW and MAX_TESS_PRIMS_PER_DRAW.

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