swr/rast: move default split size from driver to rasterizer

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

src/gallium/drivers/swr/rasterizer/codegen/knob_defs.py

@@ -138,7 +138,7 @@ KNOBS = [
 
     ['MAX_PRIMS_PER_DRAW', {
         'type'      : 'uint32_t',
-        'default'   : '2040',
+        'default'   : '49152',
         'desc'      : ['Maximum primitives in a single Draw().',
                        'Larger primitives are split into smaller Draw calls.',
                        'Should be a multiple of (3 * vectorWidth).'],

src/gallium/drivers/swr/swr_screen.cpp

@@ -1065,10 +1065,6 @@ swr_create_screen_internal(struct sw_winsys *winsys)
    if (!screen)
       return NULL;
 
-   if (!getenv("KNOB_MAX_PRIMS_PER_DRAW")) {
-      g_GlobalKnobs.MAX_PRIMS_PER_DRAW.Value(49152);
-   }
-
    if (!lp_build_init()) {
       FREE(screen);
       return NULL;