Use the newly introduced Flags<> class to store a bitfield of
File::OpenMode in a type-safe way. The existing File::OpenMode enum is
renamed to File::OpenModeFlag to free the File::OpenMode for the Flags<>
type alias.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>