No, you shouldn't. That could give the impression that you are making excuses.
Are there any other reasons for you average performance? Aspergers syndrom may give disabilities but it may also enhance your skills. That is why you should use it only to explain some of your problems, not all of them.
You shouldn't think how to explain your weaknesses, but rather how to enhance your strengths. The universities are not interested of why you performed badly, they are interested of how you can perform well in the future. You need to show them that you are ready to work hard, learn, achieve and accomplish things. Universities don't want people who live in the past, they want people who will be great in the future.
The academic world rarely cares about disabilities. If you tell them that you have autism, they will most likely treat you the same no matter what. If you want to use Aspergers syndrom, then you need to use that condition to show how you succeeded despite your disability.