example_cfu/cfu_gen.py: lazy cfu.v updating
example_cfu/cfu_gen.py: lazy cfu.v updating

Copied cfu_gen.py from proj_template so that cfu.v is only updated when
its content changes.

Signed-off-by: Alan Green <97e77871b5fcc4941bebceb4338c97c1fd149f8c@google.com>

google/CFU-Playground,google/CFU-Playground,google/CFU-Playground,google/CFU-Playground