For the purpose of testing serializing/deserializing Flags in function parameters, add an enum class TestFlags and Flags<TestFlags> to some function parameters, both for input and output and Signals. While at it, update the ipa_interface_test. Signed-off-by: Paul Elder <paul.elder@ideasonboard.com> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>