Roommates/dormmates would probably be good to tell so that they can be accommodating; I'm not sure what the purpose would be in telling classmates, though. For roommates, I'd just try to mention it casually. Like, when there's something you're doing or not doing that's connected to ASD, just mention that as the reason, but in a passing, matter-of-fact way. If you make it a big deal, then they'll make it a big deal; if you don't make it a big deal, then they probably won't, either. Mentioning it could be as simple as heading out to the library to study one day and saying something like "As an Aspie, it's so much easier for me to get work done on the quiet floor than here with chairs scraping the ceiling from the dorm above us." Just something little. If they ask more, tell more; if they don't, then you've made them aware, and you can follow up more later if needed (like when they're doing something that's problematic, you can be like "Ya know, since I'm on the spectrum, I can't deal with this the same way you can...can we compromise?").
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