softpipe: Move st/python's malloc winsys to softpipe

Users of softpipe can still specify thier own winsys
but now there is a default one also that uses malloc.
This allows the malloc winsys to be shared with other
users of softpipe.

src/gallium/drivers/softpipe/SConscript

@@ -34,6 +34,7 @@ softpipe = env.ConvenienceLibrary(
 		'sp_texture.c',
 		'sp_tile_cache.c',
 		'sp_video_context.c',
+		'sp_winsys.c'
 	])
 
 Export('softpipe')