Is there any universally accepted criterion for subordination cross -linguistically?
First, "subordination" must be defined. It is
not well defined in general, and there are many competing definitions out there.
You could start here:
http://en.wikipedia.org/wiki/Subordination_%28linguistics%29There are several related definitions, involving ideas like:
1. embedding (one clause inside another)
2. dependencies (one clause relies on another for information or grammatical function)
3. Non-independence: a subordinate clause is one that cannot be used independently.
In some cases, the line is blurry. In the prototypical cases, it's fairly obvious. This is an interesting puzzle and not one that has been solved.
Can embedding be considered such a criteria?
Yes. I think it's a good definition, because if a clause is embedded it is subordinate (I believe this is true; again, there could be room to debate). But it is not necessary that it is embedded-- probably, but maybe not. In some fuzzy cases, that's one question. So embedded => subordinate, but maybe not subordinate => embedded. Usually they're the same thing, though.
Is there any language that never use subordination at all?
Hmm... probably all languages do this. But Daniel Everett has claimed that subordination (and many other things) are not found in Pirahã.
For a while it was said that sign languages did not have subordination; this was wrong-- researchers looking at the data in a different way showed it does have subordination.
Also, if defined based on the typical Latin/European model, some languages (like Native American languages or the oldest stages of Indo-European languages) appear to lack subordination, but this is just if we assume we'll find words like "that" and so forth-- there are clearly still different kinds of subordinated/embedded clauses such as with participles and so forth.