I think it's more akin to number 1. I think the phrase came from this Adidas commercial.
Like "think different", it's another catch phrase from advertisers.
"You are nothing" means you have no value or that you are worthless -- not worth considering.
"Impossible is nothing" would mean that "impossible" should not be considered -- that is, impossible is not a possibility. What's left then is only what's possible.
That is a positive message -- that everything is possible.
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