Enforce a bit or value in enum items

Enforce a bit or value in enum items

Do not allow enum items without an explicit bit or value. The value of
an enum item is known when adding the enum to the xml specification.
There's no reason why this information shouldn't be where it belongs to.

Signed-off-by: Daniel Martin <consume.noise@gmail.com>
Reviewed-by: Ran Benita <ran234@gmail.com> (and tested)
Reviewed-by: Josh Triplett <josh@joshtriplett.org>