Currently, enums that are passed between pipeline handlers and their IPA must be defined in a mojom file. However, there is a use case for enum/flags to be defined in a C++ header, such that the enum can be used in a component other than the pipeline handler and its IPA. To support this, add support for the skipHeader attribute for enums. Like structs, it is only allowed in core.mojom. Signed-off-by: Paul Elder <paul.elder@ideasonboard.com> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>