gen2/test_hps_cfu: Refactor configuration logic
gen2/test_hps_cfu: Refactor configuration logic

Refactors configuration logic in test case so that future tests can
configure the accelerator to output a range of the output channels
instead of all of them.

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

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