tests: allow having zero gpio-mockup chips for tests
tests: allow having zero gpio-mockup chips for tests

We may have tests which don't require any gpio-mockup chips to be
present. When an empty array is given as the list of chip line counts,
the gpio-mockup module will not be loaded.

Signed-off-by: Bartosz Golaszewski <108de5fbc428215dc26df4468b48691526611148@gmail.com>

brgl/libgpiod,brgl/libgpiod,brgl/libgpiod,brgl/libgpiod