litex.build: update from migen.genlib.io litex.build.io.

examples/fast_scope_arty.py

@@ -6,9 +6,10 @@
 import sys
 
 from migen import *
-from migen.genlib.io import CRG, DifferentialInput
+from migen.genlib.io import CRG
 
 from litex.build.generic_platform import *
+from litex.build.io import DifferentialInput
 from litex.build.tools import write_to_file
 
 from litex.boards.platforms import arty