platform/chrome: cros_ec_proto: add Kunit tests for check_features

cros_ec_check_features() gets EC features if it hasn't had cache, and
checks whether the given EC_FEATURE_* is supported or not.

Add Kunit tests for cros_ec_check_features().

Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Link: https://lore.kernel.org/r/20220622041040.202737-6-tzungbi@kernel.org