net: microchip: sparx5: kunit test: change test_callbacks and test_vctrl to static

test_callbacks and test_vctrl are only used in vcap_api_kunit.c now,
change them to static.

Fixes: 67d63751

 ("net: microchip: sparx5: Adding KUNIT test for the VCAP API")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Steen Hegelund <Steen.Hegelund@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>