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>